PUBLIC SERVICE CO OF COLORADO, 10-Q filed on 4/27/2018
Quarterly Report
v3.8.0.1
Document and Entity Information - shares
 3 Months Ended
Mar. 31, 2018
Apr. 27, 2018
Document and Entity Information [Abstract]    
Entity Registrant Name PUBLIC SERVICE CO OF COLORADO  
Entity Central Index Key 0000081018  
Current Fiscal Year End Date --12-31  
Entity Well-known Seasoned Issuer Yes  
Entity Voluntary Filers No  
Entity Current Reporting Status Yes  
Entity Filer Category Non-accelerated Filer  
Document Type 10-Q  
Document Period End Date Mar. 31, 2018  
Document Fiscal Year Focus 2018  
Document Fiscal Period Focus Q1  
Amendment Flag false  
Entity Common Stock, Shares Outstanding   100
v3.8.0.1
CONSOLIDATED STATEMENTS OF INCOME (UNAUDITED) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Operating revenues    
Electric $ 698,274 $ 711,388
Natural gas 363,986 356,136
Steam and other 11,038 13,010
Total operating revenues 1,073,298 1,080,534
Operating expenses    
Electric fuel and purchased power 281,170 288,827
Cost of natural gas sold and transported 191,265 196,402
Cost of sales — steam and other 3,876 4,386
Operating and maintenance expenses 183,075 185,088
Demand side management expenses 32,752 28,104
Depreciation and amortization 121,607 114,994
Taxes (other than income taxes) 52,657 49,798
Total operating expenses 866,402 867,599
Operating income 206,896 212,935
Other income, net 231 3,204
Allowance for funds used during construction — equity 10,944 4,608
Interest charges and financing costs    
Interest charges — includes other financing costs of $1,572 and $1,521, respectively 49,921 45,882
Allowance for funds used during construction — debt (4,581) (1,906)
Total interest charges and financing costs 45,340 43,976
Income before income taxes 172,731 176,771
Income taxes 39,009 65,225
Net income $ 133,722 $ 111,546
v3.8.0.1
CONSOLIDATED STATEMENTS OF INCOME (UNAUDITED) (Parenthetical) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Interest charges and financing costs    
Other financing costs $ 1,572 $ 1,521
v3.8.0.1
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Comprehensive income:    
Net income $ 133,722 $ 111,546
Amortization of losses included in net periodic benefit cost, net of tax of $1, and $1, respectively 2 1
Derivative instruments:    
Reclassification of losses to net income, net of tax of $98 and $152, respectively 300 246
Other comprehensive income 302 247
Comprehensive income $ 134,024 $ 111,793
v3.8.0.1
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) (Parenthetical) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Derivative instruments:    
Reclassification of losses (gains) to net income, tax $ 98 $ 152
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, Tax $ 1 $ 1
v3.8.0.1
CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Operating activities    
Net income $ 133,722 $ 111,546
Adjustments to reconcile net income to cash provided by operating activities:    
Depreciation and amortization 122,802 115,803
Demand side management program amortization 0 336
Deferred income taxes 13,168 61,726
Amortization of investment tax credits (700) (701)
Allowance for equity funds used during construction (10,944) (4,608)
Net realized and unrealized hedging and derivative transactions 1,807 1,679
Changes in operating assets and liabilities:    
Accounts receivable (19,358) 1,086
Accrued unbilled revenues 58,369 91,100
Inventories 60,563 43,667
Prepayments and other 1,330 659
Accounts payable (25,773) (65,886)
Net regulatory assets and liabilities 31,072 14,345
Other current liabilities 465 17,860
Pension and other employee benefit obligations (22,803) (16,506)
Change in other noncurrent assets 2,465 936
Change in other noncurrent liabilities (7,435) 479
Net cash provided by operating activities 338,750 373,521
Investing activities    
Utility capital/construction expenditures (426,730) (272,927)
Allowance for equity funds used during construction 10,944 4,608
Investments in utility money pool arrangement (36,000) (38,000)
Repayments from utility money pool arrangement 56,000 38,000
Net cash used in investing activities (395,786) (268,319)
Financing activities    
Repayments of short-term borrowings, net 95,000 (98,000)
Borrowings under utility money pool arrangement 158,000 40,000
Repayments under utility money pool arrangement (110,000) (40,000)
Capital contributions from parent 6,508 67,475
Dividends paid to parent (76,195) (74,208)
Other (117) (110)
Net cash provided by (used in) financing activities 73,196 (104,843)
Net change in cash and cash equivalents 16,160 359
Cash and cash equivalents at beginning of period 7,513 5,926
Cash and cash equivalents at end of period 23,673 6,285
Supplemental disclosure of cash flow information:    
Cash paid for interest (net of amounts capitalized) (60,064) (61,252)
Cash paid for income taxes, net (46,482) (4,804)
Supplemental disclosure of non-cash investing transactions:    
Property, plant and equipment additions in accounts payable $ 128,493 $ 69,885
v3.8.0.1
CONSOLIDATED BALANCE SHEETS (UNAUDITED) - USD ($)
$ in Thousands
Mar. 31, 2018
Dec. 31, 2017
Current assets    
Cash and cash equivalents $ 23,673 $ 7,513
Accounts receivable, net 312,526 294,403
Accounts receivable from affiliates 9,446 14,719
Investments in utility money pool arrangement 0 20,000
Accrued unbilled revenues 237,432 295,801
Inventories 153,926 214,489
Regulatory assets 68,164 77,337
Derivative instruments 4,897 3,197
Prepayments and other 34,390 35,720
Total current assets 844,454 963,179
Property, plant and equipment, net 14,291,475 14,025,751
Other assets    
Regulatory assets 945,739 950,258
Derivative instruments 1,093 1,009
Other 24,494 27,429
Total other assets 971,326 978,696
Total assets 16,107,255 15,967,626
Current liabilities    
Current portion of long-term debt 305,721 305,577
Short-term debt 95,000 0
Borrowings Payable Under Utility Money Pool Arrangement 48,000 0
Accounts payable 430,515 492,829
Accounts payable to affiliates 38,830 58,749
Regulatory liabilities 79,080 66,126
Taxes accrued 249,359 222,517
Accrued interest 33,640 48,552
Dividends payable to parent 95,351 76,195
Derivative instruments 7,344 7,348
Other 82,041 92,333
Total current liabilities 1,464,881 1,370,226
Deferred credits and other liabilities    
Deferred income taxes 1,661,220 1,644,476
Deferred investment tax credits 27,158 27,858
Regulatory liabilities 1,943,401 1,933,488
Asset retirement obligations 351,379 347,769
Derivative instruments 2,367 3,468
Customer Advances for Construction 170,262 162,614
Pension and employee benefit obligations 264,668 287,783
Other 52,819 58,923
Total deferred credits and other liabilities 4,473,274 4,466,379
Commitments and contingencies
Capitalization    
Long-term debt 4,302,104 4,302,698
Common stock — 100 shares authorized at $0.01 par value; 100 shares outstanding at March 31, 2018 and Dec. 31, 2017, respectively 0 0
Additional paid in capital 4,032,826 4,032,826
Retained earnings 1,860,600 1,822,229
Accumulated other comprehensive loss (26,430) (26,732)
Total common stockholder’s equity 5,866,996 5,828,323
Total liabilities and equity $ 16,107,255 $ 15,967,626
v3.8.0.1
CONSOLIDATED BALANCE SHEETS (UNAUDITED) (Parenthetical) - $ / shares
Mar. 31, 2018
Dec. 31, 2017
Capitalization, Long-term Debt and Equity [Abstract]    
Common stock, shares authorized (in shares) 100 100
Common stock, par value (in dollars per share) $ 0.01 $ 0.01
Common stock, shares outstanding (in shares) 100 100
v3.8.0.1
Management's Opinion
 3 Months Ended
Mar. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]  
Management's Opinion
In the opinion of management, the accompanying unaudited consolidated financial statements contain all adjustments necessary to present fairly, in accordance with accounting principles generally accepted in the United States of America (GAAP), the financial position of PSCo and its subsidiaries as of March 31, 2018 and Dec. 31, 2017; the results of its operations, including the components of net income and comprehensive income, for the three months ended March 31, 2018 and 2017; and its cash flows for the three months ended March 31, 2018 and 2017. All adjustments are of a normal, recurring nature, except as otherwise disclosed. Management has also evaluated the impact of events occurring after March 31, 2018 up to the date of issuance of these consolidated financial statements. These statements contain all necessary adjustments and disclosures resulting from that evaluation. The Dec. 31, 2017 balance sheet information has been derived from the audited 2017 consolidated financial statements included in the PSCo Annual Report on Form 10-K for the year ended Dec. 31, 2017. These notes to the consolidated financial statements have been prepared pursuant to the rules and regulations of the SEC for Quarterly Reports on Form 10-Q. Certain information and note disclosures normally included in financial statements prepared in accordance with GAAP on an annual basis have been condensed or omitted pursuant to such rules and regulations. For further information, refer to the consolidated financial statements and notes thereto, included in the PSCo Annual Report on Form 10-K for the year ended Dec. 31, 2017, filed with the SEC on Feb. 23, 2018. Due to the seasonality of PSCo’s electric and natural gas sales, interim results are not necessarily an appropriate base from which to project annual results.
v3.8.0.1
Summary of Significant Accounting Policies
 3 Months Ended
Mar. 31, 2018
Accounting Policies [Abstract]  
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies

The significant accounting policies set forth in Note 1 to the consolidated financial statements in the PSCo Annual Report on Form 10-K for the year ended Dec. 31, 2017, appropriately represent, in all material respects, the current status of accounting policies and are incorporated herein by reference.
v3.8.0.1
Accounting Pronouncements
 3 Months Ended
Mar. 31, 2018
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]  
Accounting Pronouncements
Accounting Pronouncements

Recently Issued

Leases — In February 2016, the Financial Accounting Standards Board (FASB) issued Leases, Topic 842 (Accounting Standards Update (ASU) No. 2016-02), which for lessees requires balance sheet recognition of right-of-use assets and lease liabilities for most leases. This guidance will be effective for interim and annual reporting periods beginning after Dec. 15, 2018. PSCo has not yet fully determined the impacts of implementation. However, adoption is expected to occur on Jan. 1, 2019 utilizing the practical expedients provided by the standard and proposed in Targeted Improvements, Topic 842 (Proposed ASU 2018-200). As such, agreements entered into prior to Jan. 1, 2019 that are currently considered leases are expected to be recognized on the consolidated balance sheet, including contracts for use of office space, equipment and natural gas storage assets, as well as certain purchased power agreements (PPAs) for natural gas-fueled generating facilities. PSCo expects that similar agreements entered into after Dec. 31, 2018 will generally qualify as leases under the new standard.

Recently Adopted

Revenue Recognition — In May 2014, the FASB issued Revenue from Contracts with Customers, Topic 606 (ASU No. 2014-09), which provides a new framework for the recognition of revenue. PSCo implemented the guidance on a modified retrospective basis on Jan. 1, 2018. Results for reporting periods beginning after Dec. 31, 2017 are presented in accordance with Topic 606, while prior period results have not been adjusted and continue to be reported in accordance with prior accounting guidance. Other than increased disclosures regarding revenues related to contracts with customers, the implementation did not have a significant impact on PSCo’s consolidated financial statements. For related disclosures, see Note 13.

Classification and Measurement of Financial Instruments — In January 2016, the FASB issued Recognition and Measurement of Financial Assets and Financial Liabilities, Subtopic 825-10 (ASU No. 2016-01), which eliminated the available-for-sale classification for marketable equity securities and also replaced the cost method of accounting for non-marketable equity securities with a model for recognizing impairments and observable price changes. Under the new standard, other than when the consolidation or equity method of accounting is utilized, changes in the fair value of equity securities are recognized in earnings. PSCo implemented the guidance on Jan. 1, 2018 and the implementation did not have a material impact on its consolidated financial statements.

Presentation of Net Periodic Benefit Cost — In March 2017, the FASB issued Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost, Topic 715 (ASU No. 2017-07), which establishes that only the service cost element of pension cost may be presented as a component of operating income in the income statement. Also under the guidance, only the service cost component of pension cost is eligible for capitalization. As a result of application of accounting principles for rate regulated entities, a similar amount of pension cost, including non-service components, will be recognized consistent with the historical ratemaking treatment, and the impacts of adoption will be limited to changes in classification of non-service costs in the consolidated statement of income. PSCo implemented the new guidance on Jan. 1, 2018, and as a result, $0.5 million of pension costs were retrospectively reclassified from operating and maintenance expenses to other income, net on the consolidated income statement for the three months ended March 31, 2017. Under a practical expedient permitted by the standard, PSCo used benefit cost amounts disclosed for prior periods as the basis for retrospective application.
v3.8.0.1
Selected Balance Sheet Data
 3 Months Ended
Mar. 31, 2018
Balance Sheet Related Disclosures [Abstract]  
Selected Balance Sheet Data
Selected Balance Sheet Data
(Thousands of Dollars)
 
March 31, 2018
 
Dec. 31, 2017
Accounts receivable, net
 
 
 
 
Accounts receivable
 
$
332,506

 
$
314,009

Less allowance for bad debts
 
(19,980
)
 
(19,606
)
 
 
$
312,526

 
$
294,403


(Thousands of Dollars)
 
March 31, 2018
 
Dec. 31, 2017
Inventories
 
 
 
 
Materials and supplies
 
$
69,378

 
$
68,940

Fuel
 
53,282

 
73,893

Natural gas
 
31,266

 
71,656

 
 
$
153,926

 
$
214,489


(Thousands of Dollars)
 
March 31, 2018
 
Dec. 31, 2017
Property, plant and equipment, net
 
 
 
 
Electric plant
 
$
12,692,880

 
$
12,627,592

Natural gas plant
 
4,140,582

 
4,102,075

Common and other property
 
1,031,570

 
1,022,333

Plant to be retired (a)
 
10,627

 
10,949

Construction work in progress
 
1,264,835

 
1,014,338

Total property, plant and equipment
 
19,140,494

 
18,777,287

Less accumulated depreciation
 
(4,849,019
)
 
(4,751,536
)
 
 
$
14,291,475

 
$
14,025,751



(a) 
In the third quarter of 2017, PSCo early retired Valmont Unit 5 and converted Cherokee Unit 4 from a coal-fueled generating facility to natural gas. PSCo also expects Craig Unit 1 to be early retired in approximately 2025. Amounts are presented net of accumulated depreciation.
v3.8.0.1
Income Taxes
 3 Months Ended
Mar. 31, 2018
Income Tax Disclosure [Abstract]  
Income Taxes
Income Taxes

Except to the extent noted below, Note 7 to the consolidated financial statements included in PSCo’s Annual Report on Form 10-K for the year ended Dec. 31, 2017 appropriately represents, in all material respects, the current status of other income tax matters, and are incorporated herein by reference.

Total income tax expense from operations differs from the amount computed by applying the statutory federal income tax rate to income before income tax expense. The following reconciles such differences:
 
Three Months ended March 31
 
 
2018
 
2017
Federal statutory rate
 
21.0
 %
 
35.0
 %
State tax, net of federal tax effect
 
3.7

 
3.0

Increases (decreases) in tax from:
 
 
 
 
Regulatory differences - ARAM (a)
(3.3
)
 
(0.1
)
Regulatory differences - ARAM deferral (b)
3.1

 
—

Regulatory differences - other utility plant items
(1.3
)
 
(0.4
)
Other tax credits, net of federal income tax expense
(1.0
)
 
(0.7
)
Other, net
0.4

 
0.1

Effective income tax rate
 
22.6
 %
 
36.9
 %

(a)  
The average rate assumption method (ARAM); a method to flow back excess deferred taxes to customers.
(b)
As we receive further clarity or direction from our commissions regarding the flow back to customers of excess deferred taxes resulting from the TCJA, the ARAM deferral may decrease during the year, which would result in a reduction to tax expense with a correlating reduction to revenue.

Federal Audits — PSCO is a member of the Xcel Energy affiliated group that files a consolidated federal income tax return. The statute of limitations applicable to Xcel Energy’s federal income tax returns expire as follows:
Tax Year(s)
 
Expiration
2009 - 2011
 
December 2018
2012 - 2013
 
October 2018
2014
 
September 2018
2015
 
September 2019
2016
 
September 2020


In 2012, the Internal Revenue Service (IRS) commenced an examination of tax years 2010 and 2011, including the 2009 carryback claim. The IRS proposed an adjustment to the federal tax loss carryback claims and in 2015, the IRS forwarded the issue to the Office of Appeals (“Appeals”). In 2017 Xcel Energy and Appeals reached an agreement and the benefit related to the agreed upon portions was recognized. PSCo did not accrue any income tax benefit related to this adjustment. As of March 31, 2018, the case has been forwarded to the Joint Committee on Taxation.

In the third quarter of 2015, the IRS commenced an examination of tax years 2012 and 2013. In the third quarter of 2017, the IRS concluded the audit of tax years 2012 and 2013 and proposed an adjustment that would impact Xcel Energy’s net operating loss (NOL) and effective tax rate (ETR). After evaluating the proposed adjustment Xcel Energy filed a protest with the IRS. Xcel Energy anticipates the issue will be forwarded to Appeals. As of March 31, 2018, Xcel Energy has recognized its best estimate of income tax expense that will result from a final resolution of this issue; however, the outcome and timing of a resolution is uncertain.

State Audits — PSCo is a member of the Xcel Energy affiliated group that files consolidated state income tax returns. As of March 31, 2018, PSCo’s earliest open tax year that is subject to examination by state taxing authorities under applicable statutes of limitations is 2009. There are currently no state income tax audits in progress.

Unrecognized Benefits — The unrecognized tax benefit balance includes permanent tax positions, which if recognized would affect the annual ETR. In addition, the unrecognized tax benefit balance includes temporary tax positions for which the ultimate deductibility is highly certain but for which there is uncertainty about the timing of such deductibility. A change in the period of deductibility would not affect the ETR but would accelerate the payment of cash to the taxing authority to an earlier period.

A reconciliation of the amount of unrecognized tax benefit is as follows:
(Millions of Dollars)
 
March 31, 2018
 
Dec. 31, 2017
Unrecognized tax benefit — Permanent tax positions
 
$
4.1

 
$
4.0

Unrecognized tax benefit — Temporary tax positions
 
6.0

 
6.1

Total unrecognized tax benefit
 
$
10.1

 
$
10.1



The unrecognized tax benefit amounts were reduced by the tax benefits associated with NOL and tax credit carryforwards. The amounts of tax benefits associated with NOL and tax credit carryforwards are as follows:
(Millions of Dollars)
 
March 31, 2018
 
Dec. 31, 2017
NOL and tax credit carryforwards
 
$
(4.2
)
 
$
(4.0
)


It is reasonably possible that PSCo’s amount of unrecognized tax benefits could significantly change in the next 12 months as the IRS Appeals progresses and the IRS and state audits resume. As the IRS Appeals progresses, it is reasonably possible that the amount of unrecognized tax benefit could decrease up to approximately $6 million.

The payable for interest related to unrecognized tax benefits is partially offset by the interest benefit associated with NOL and tax credit carryforwards. The payables for interest related to unrecognized tax benefits at March 31, 2018, and Dec. 31, 2017 were not material. No amounts were accrued for penalties related to unrecognized tax benefits as of March 31, 2018 or Dec. 31, 2017.
v3.8.0.1
Rate Matters
 3 Months Ended
Mar. 31, 2018
Public Utilities, General Disclosures [Abstract]  
Rate Matters
Rate Matters

Except to the extent noted below, the circumstances set forth in Note 11 to the consolidated financial statements included in PSCo’s Annual Report on Form 10-K for the year ended Dec. 31, 2017, appropriately represent, in all material respects, the current status of other rate matters, and are incorporated herein by reference.

Tax Reform — Regulatory Proceedings

The specific impacts of the Tax Cuts and Jobs Act (TCJA) on customer rates are subject to regulatory approval. Each of the states in Xcel Energy’s service areas, including Colorado, have opened dockets to address the impacts of the TCJA. PSCo has made filings and is working with various stakeholders to determine the appropriate treatment for the TCJA.

In January 2018, the Colorado Public Utilities Commission (CPUC) opened a statewide TCJA proceeding and ordered deferred accounting for all investor-owned utilities.

•
Colorado 2017 Multi-Year Natural Gas Rate Case - In February 2018, the administrative law judge (ALJ) approved PSCo and the CPUC Staff’s settlement agreement addressing the TCJA, which includes a $20 million reduction to provisional rates effective March 1, 2018. A final true-up, including any outcomes associated with the statewide proceeding, would provide customers the full net benefit of the TCJA effective January 2018. A CPUC decision is pending.

•
Colorado Electric - In April 2018, PSCo, the CPUC Staff and the OCC filed a TCJA settlement agreement with the CPUC that identified a reduction in electric revenue requirements of approximately $101 million for the TCJA in 2018.  The settlement recommended a customer refund of $42 million in 2018, with the remainder of $59 million be used to accelerate the amortization of an existing prepaid pension asset.  With the dismissal of the 2017 rate case, revisions to the TCJA settlement are required to address the impacts of the TCJA for 2019 until new base rates go into effect in connection with a future electric rate case that PSCo anticipates filing later this summer. A CPUC decision is pending.

Federal Energy Regulatory Commission (FERC) Formula Rates — The FERC has not yet issued guidance on how or when electric utilities should reflect the impacts of the TCJA in FERC jurisdictional wholesale rates. The FERC issued a Notice of Inquiry (NOI) in March 2018 seeking comments on how to reflect the TCJA impacts in wholesale rates, in particular changes to accumulated deferred income taxes and bonus depreciation. Comments for the NOI are due in May 2018. However, FERC-approved formula rates for wholesale customers are generally adjusted on an annual basis for certain changes in rate base and actual operating expenses, including income taxes. As a result, these revenues would be subject to an automatic reduction for the effect of the TCJA corporate tax rate change through the annual true-up process, absent specific FERC action.

In February 2018, PSCo made a filing with FERC requesting early reductions in its transmission and production formula rates in 2018 for corporate tax rate impacts of the TCJA. In March 2018, the FERC issued an order granting PSCo’s waiver request so that 2018 rates will reflect the lower federal corporate tax rate.

Pending Regulatory Proceedings — CPUC

Colorado 2017 Multi-Year Electric Rate Case — In October 2017, PSCo filed a multi-year request with the CPUC seeking to increase electric rates approximately $245 million over four years. The request was based on forecast test years (FTY), a 10.0 percent return on equity (ROE) and an equity ratio of 55.25 percent. Interim rates, subject to refund and interest, were to be effective on June 1, 2018.
Revenue Request (Millions of Dollars)
 
2018
 
2019
 
2020
 
2021
 
Total
Revenue request
 
$
74

 
$
75

 
$
60

 
$
36

 
$
245

Clean Air Clean Jobs Act (CACJA) rider conversion to base rates
 
90

 
—

 
—

 
—

 
90

Transmission Cost Adjustment (TCA) rider conversion to base rates
 
43

 
—

 
—

 
—

 
43

  Total
 
$
207

 
$
75

 
$
60

 
$
36

 
$
378

 
 
 
 
 
 
 
 
 
 
 
Expected year-end rate base (billions of dollars)
 
$
6.8

 
$
7.1

 
$
7.3

 
$
7.4

 
 

     
In March 2018, PSCo, CPUC Staff and OCC reached a settlement and filed a motion with the CPUC requesting changes to the procedural schedule and scope of the electric case, which included delaying the implementation of provisional rates from June 2018 to January 2019 and requiring PSCo to file updated test year information for 2019-2021 which included the impacts of TCJA. In April 2018, the CPUC denied the motion on procedural grounds and dismissed the electric rate case. PSCo anticipates filing a new electric rate case in the summer of 2018 with new rates expected to be effective in the first quarter of 2019.

Colorado 2017 Multi-Year Natural Gas Rate Case — In June 2017, PSCo filed a multi-year request with the CPUC seeking to increase retail natural gas rates approximately $139 million over three years. The request, detailed below, is based on FTYs, a 10.0 percent ROE and an equity ratio of 55.25 percent.
Revenue Request (Millions of Dollars)
 
2018
 
2019
 
2020
 
Total
Revenue request
 
$
63

 
$
33

 
$
43

 
$
139

Pipeline System Integrity Adjustment (PSIA) rider conversion to base rates (a)
 
—

 
94

 
—

 
94

Total
 
$
63

 
$
127

 
$
43

 
$
233

 
 
 
 
 
 
 
 
 
Expected year-end rate base (billions of dollars) (b)
 
$
1.5

 
$
2.3

 
$
2.4

 
 
 
(a)  
The roll-in of PSIA rider revenue into base rates will not have an impact on customer bills or revenue as these costs are already being recovered through the rider. The recovery of incremental PSIA related investments in 2019 and 2020 are included in the base rate request.
(b)  
The additional rate base in 2019 predominantly reflects the roll-in of capital associated with the PSIA rider.

In October 2017, the CPUC Staff and the OCC recommended a single 2016 historic test year (HTY) based on an average 13-month rate base, and opposed a multi-year request. In addition, they recommended an equity ratio of 48.73 percent and 51.2 percent, respectively, and the existing PSIA rider expire with the 2018 rates rolled into base rates beginning Jan. 1, 2019. Planned investments in 2019 and 2020 would be recoverable through a future rate case. The Staff and OCC provide for a recommended 2018 rate increase of approximately $30 million and $39 million, respectively.

Provisional rates, subject to refund, of $63 million were implemented on Jan. 1, 2018.

On Jan. 31, 2018, the CPUC ordered deferred accounting for the impacts of TCJA and opened a statewide TCJA proceeding, as discussed below. In February 2018, the ALJ approved a settlement agreement between PSCo and the CPUC, which reduced provisional rates by $20 million to address the impacts of the TCJA. The CPUC is expected to rule on the regulatory treatment of the TCJA and the natural gas rate case later in 2018.

On April 20, 2018, PSCo filed for a PSIA extension through 2020 in the event that the CPUC does not adopt its multi-year plan proposal.
v3.8.0.1
Commitments and Contingencies
 3 Months Ended
Mar. 31, 2018
Commitments and Contingencies Disclosure [Abstract]  
Commitments and Contingencies
Commitments and Contingencies

Except to the extent noted below and in Note 5 above, the circumstances set forth in Notes 11 and 12 to the consolidated financial statements included in PSCo’s Annual Report on Form 10-K for the year ended Dec. 31, 2017, appropriately represent, in all material respects, the current status of commitments and contingent liabilities and are incorporated herein by reference. The following include commitments, contingencies and unresolved contingencies that are material to PSCo’s financial position.

PPAs

Under certain PPAs, PSCo purchases power from independent power producing entities that own natural gas fueled power plants for which PSCo is required to reimburse natural gas fuel costs, or to participate in tolling arrangements under which PSCo procures the natural gas required to produce the energy that it purchases. These specific PPAs create a variable interest in the associated independent power producing entity.

PSCo had approximately 1,571 megawatts (MW) of capacity under long-term PPAs as of March 31, 2018 and Dec. 31, 2017, with entities that have been determined to be variable interest entities. PSCo has concluded that these entities are not required to be consolidated in its consolidated financial statements because it does not have the power to direct the activities that most significantly impact the entities’ economic performance. These agreements have expiration dates through 2032.

Environmental Contingencies

Manufactured Gas Plant (MGP), Landfill or Disposal Sites — PSCo is currently involved in investigating and/or remediating several MGP, landfill or other disposal sites. PSCo has identified two sites where contamination is present and where investigation and/or remediation activities are currently underway. Other parties may have responsibility for some portion of the investigation and/or remediation activities that are underway. PSCo anticipates that these investigation or remediation activities will continue through at least 2018. PSCo had accrued $1 million as of March 31, 2018 and an immaterial amount as of Dec. 31, 2017, for these sites. There may be insurance recovery and/or recovery from other potentially responsible parties that will offset any costs incurred. PSCo anticipates that any amounts spent will be fully recovered from customers.

Legal Contingencies

PSCo is involved in various litigation matters that are being defended and handled in the ordinary course of business. The assessment of whether a loss is probable or is a reasonable possibility, and whether the loss or a range of loss is estimable, often involves a series of complex judgments about future events. Management maintains accruals for such losses that are probable of being incurred and subject to reasonable estimation. Management is sometimes unable to estimate an amount or range of a reasonably possible loss in certain situations, including but not limited to when (1) the damages sought are indeterminate, (2) the proceedings are in the early stages, or (3) the matters involve novel or unsettled legal theories. In such cases, there is considerable uncertainty regarding the timing or ultimate resolution of such matters, including a possible eventual loss. For current proceedings not specifically reported herein, management does not anticipate that the ultimate liabilities, if any, arising from such current proceedings would have a material effect on PSCo’s financial statements. Unless otherwise required by GAAP, legal fees are expensed as incurred.

Employment, Tort and Commercial Litigation

Line Extension Disputes — In December 2015, Development Recovery Company (DRC) filed a lawsuit in the Denver District Court, stating PSCo failed to award proper allowances and refunds for line extensions to new developments pursuant to the terms of electric and gas service agreements entered into by PSCo and various developers. The dispute involved claims by over fifty developers. In February 2018, the Colorado Supreme Court denied DRC’s petition to appeal the Denver District Court’s dismissal of the lawsuit, effectively terminating this litigation. However, in January 2018, DRC filed a new lawsuit in Boulder County District Court, asserting a single claim that PSCo was required to file its line extension agreements with the CPUC but failed to do so. This claim is substantially similar to the arguments previously raised by DRC. In February 2018, PSCo filed a motion to dismiss. Dates for this proceeding have not been scheduled.

PSCo has concluded that a loss is remote with respect to this matter as the service agreements were developed to implement CPUC approved tariffs and PSCo has complied with the tariff provisions. Also, if a loss were sustained, PSCo believes it would be allowed to recover these costs through traditional regulatory mechanisms. The amount or range in dispute is presently unknown and no accrual has been recorded for this matter.
v3.8.0.1
Borrowings and Other Financing Instruments
 3 Months Ended
Mar. 31, 2018
Debt Disclosure [Abstract]  
Borrowings and Other Financing Instruments
Borrowings and Other Financing Instruments

Short-Term Borrowings

Money Pool — Xcel Energy Inc. and its utility subsidiaries have established a money pool arrangement that allows for short-term investments in and borrowings between the utility subsidiaries. Xcel Energy Inc. may make investments in the utility subsidiaries at market-based interest rates; however, the money pool arrangement does not allow the utility subsidiaries to make investments in Xcel Energy Inc. Money pool borrowings for PSCo were as follows:
(Amounts in Millions, Except Interest Rates)
 
Three Months Ended March 31, 2018
 
Year Ended Dec. 31, 2017
Borrowing limit
 
$
250

 
$
250

Amount outstanding at period end
 
48

 
—

Average amount outstanding
 
12

 
—

Maximum amount outstanding
 
97

 
20

Weighted average interest rate, computed on a daily basis
 
1.64
%
 
0.92
%
Weighted average interest rate at period end
 
1.64

 
N/A



Commercial Paper — PSCo meets its short-term liquidity requirements primarily through the issuance of commercial paper and borrowings under its credit facility and the money pool. Commercial paper outstanding for PSCo was as follows:
(Amounts in Millions, Except Interest Rates)
 
Three Months Ended March 31, 2018
 
Year Ended Dec. 31, 2017
Borrowing limit
 
$
700

 
$
700

Amount outstanding at period end
 
95

 
—

Average amount outstanding
 
50

 
54

Maximum amount outstanding
 
151

 
268

Weighted average interest rate, computed on a daily basis
 
1.82
%
 
1.08
%
Weighted average interest rate at period end
 
2.28

 
N/A



Letters of Credit — PSCo uses letters of credit, generally with terms of one year, to provide financial guarantees for certain operating obligations. At March 31, 2018 and Dec. 31, 2017, there were $4 million and $3 million, respectively of letters of credit outstanding under the credit facility. The contract amounts of these letters of credit approximate their fair value and are subject to fees.

Credit Facility — In order to use its commercial paper program to fulfill short-term funding needs, PSCo must have a revolving credit facility in place at least equal to the amount of its commercial paper borrowing limit and cannot issue commercial paper in an aggregate amount exceeding available capacity under this credit facility. The credit facility provides short-term financing in the form of notes payable to banks, letters of credit and back-up support for commercial paper borrowings.

At March 31, 2018, PSCo had the following committed credit facility available (in millions of dollars):
Credit Facility (a)
 
Drawn (b)
 
Available
$
700

 
$
99

 
$
601


(a)    This credit facility expires in June 2021.
(b)    Includes outstanding commercial paper and letters of credit.

All credit facility bank borrowings, outstanding letters of credit and outstanding commercial paper reduce the available capacity under the credit facility. PSCo had no direct advances on the credit facility outstanding at March 31, 2018 and Dec. 31, 2017.
v3.8.0.1
Fair Value of Financial Assets and Liabilities
 3 Months Ended
Mar. 31, 2018
Fair Value Disclosures [Abstract]  
Fair Value of Financial Assets and Liabilities
Fair Value of Financial Assets and Liabilities

Fair Value Measurements

The accounting guidance for fair value measurements and disclosures provides a single definition of fair value and requires certain disclosures about assets and liabilities measured at fair value. A hierarchical framework for disclosing the observability of the inputs utilized in measuring assets and liabilities at fair value is established by this guidance. The three levels in the hierarchy are as follows:

Level 1 — Quoted prices are available in active markets for identical assets or liabilities as of the reporting date. The types of assets and liabilities included in Level 1 are highly liquid and actively traded instruments with quoted prices.

Level 2 — Pricing inputs are other than quoted prices in active markets, but are either directly or indirectly observable as of the reporting date. The types of assets and liabilities included in Level 2 are typically either comparable to actively traded securities or contracts, or priced with models using highly observable inputs.

Level 3 — Significant inputs to pricing have little or no observability as of the reporting date. The types of assets and liabilities included in Level 3 are those valued with models requiring significant management judgment or estimation.

Specific valuation methods include the following:

Cash equivalents — The fair values of cash equivalents are generally based on cost plus accrued interest; money market funds are measured using quoted net asset value.

Interest rate derivatives — The fair values of interest rate derivatives are based on broker quotes that utilize current market interest rate forecasts.

Commodity derivatives — The methods used to measure the fair value of commodity derivative forwards and options utilize forward prices and volatilities, as well as pricing adjustments for specific delivery locations, and are generally assigned a Level 2 classification. When contractual settlements extend to periods beyond those readily observable on active exchanges or quoted by brokers, the significance of the use of less observable forecasts of long-term forward prices and volatilities on a valuation is evaluated, and may result in Level 3 classification.

Derivative Instruments Fair Value Measurements

PSCo enters into derivative instruments, including forward contracts, futures, swaps and options, for trading purposes and to manage risk in connection with changes in interest rates, utility commodity prices and vehicle fuel prices.

Interest Rate Derivatives — PSCo enters into various instruments that effectively fix the interest payments on certain floating rate debt obligations or effectively fix the yield or price on a specified benchmark interest rate for an anticipated debt issuance for a specific period. These derivative instruments are generally designated as cash flow hedges for accounting purposes.

At March 31, 2018, accumulated other comprehensive losses related to interest rate derivatives included $1.2 million of net losses expected to be reclassified into earnings during the next 12 months as the related hedged interest rate transactions impact earnings, including forecasted amounts for unsettled hedges, as applicable.

Wholesale and Commodity Trading Risk — PSCo conducts various wholesale and commodity trading activities, including the purchase and sale of electric capacity, energy, energy-related instruments and natural gas related instruments, including derivatives. PSCo’s risk management policy allows management to conduct these activities within guidelines and limitations as approved by its risk management committee, which is made up of management personnel not directly involved in the activities governed by this policy.

Commodity Derivatives — PSCo enters into derivative instruments to manage variability of future cash flows from changes in commodity prices in its electric and natural gas operations, as well as for trading purposes. This could include the purchase or sale of energy or energy-related products, natural gas to generate electric energy, natural gas for resale, and vehicle fuel.

PSCo enters into derivative instruments that mitigate commodity price risk on behalf of electric and natural gas customers but may not be designated as qualifying hedging transactions. Changes in the fair value of non-trading commodity derivative instruments are recorded in other comprehensive income or deferred as a regulatory asset or liability. The classification as a regulatory asset or liability is based on commission approved regulatory recovery mechanisms. PSCo had no income related to the ineffectiveness of cash flow hedges for the three months ended March 31, 2018 and 2017.

Additionally, PSCo enters into commodity derivative instruments for trading purposes not directly related to commodity price risks associated with serving its electric and natural gas customers. Changes in the fair value of these commodity derivatives are recorded in electric operating revenues, net of amounts credited to customers under margin-sharing mechanisms.

The following table details the gross notional amounts of commodity forwards and options at March 31, 2018 and Dec. 31, 2017:
(Amounts in Thousands) (a)(b)
 
March 31, 2018
 
Dec. 31, 2017
Megawatt hours of electricity
 
21,657

 
22,260

Million British thermal units of natural gas
 
11,780

 
13,410


(a) 
Amounts are not reflective of net positions in the underlying commodities.
(b) 
Notional amounts for options are included on a gross basis, but are weighted for the probability of exercise.

The following tables detail the impact of derivative activity during the three months ended March 31, 2018 and 2017 on accumulated other comprehensive loss, regulatory assets and liabilities, and income:
 
 
Three Months Ended March 31, 2018
 
 
 
Pre-Tax Fair Value
Losses Recognized
During the Period in:
 
Pre-Tax Losses
Reclassified into Income
During the Period from:
 
 
 
(Thousands of Dollars)
 
Accumulated
Other
Comprehensive
Loss
 
Regulatory
(Assets) and
Liabilities
 
Accumulated
Other
Comprehensive
Loss
 
Regulatory
Assets and
(Liabilities)
 
Pre-Tax Gains (Losses)
Recognized
During the Period
in Income
 
Derivatives designated as cash flow hedges
 
 
 
 
 
 
 
 
 
 
 
Interest rate
 
$
—

 
$
—

 
$
398

(a) 
$
—

 
$
—

 
Total
 
$
—

 
$
—

 
$
398

 
$
—

 
$
—

 
Other derivative instruments
 
 
 
 
 
 
 
 
 
 
 
Commodity trading
 
$
—

 
$
—

 
$
—

 
$
—

 
$
524

(b) 
Natural gas commodity
 
—

 
(171
)
 
—

 
2,749

(c) 
(1,581
)
(c) 
Total
 
$
—

 
$
(171
)
 
$
—

 
$
2,749

 
$
(1,057
)
 
 
 
 
 
 
 
 
 
 
 
 
 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
Three Months Ended March 31, 2017
 
 
 
Pre-Tax Fair Value
Losses Recognized
During the Period in:
 
Pre-Tax Losses
Reclassified into Income
During the Period from:
 
 
 
(Thousands of Dollars)
 
Accumulated
Other
Comprehensive
Loss
 
Regulatory
(Assets) and
Liabilities
 
Accumulated
Other
Comprehensive
Loss
 
Regulatory
Assets and
(Liabilities)
 
Pre-Tax Gains (Losses)
Recognized
During the Period
in Income
 
Derivatives designated as cash flow hedges
 
 
 
 
 
 
 
 
 
 
 
Interest rate
 
$
—

 
$
—

 
$
398

(a) 
$
—

 
$
—

 
Total
 
$
—

 
$
—

 
$
398

 
$
—

 
$
—

 
Other derivative instruments
 
 
 
 
 
 
 
 
 
 
 
Commodity trading
 
$
—

 
$
—

 
$
—

 
$
—

 
$
379

(b) 
Natural gas commodity
 
—

 
(5,387
)
 
—

 
282

(c) 
(2,990
)
(c) 
Total
 
$
—

 
$
(5,387
)
 
$
—

 
$
282

 
$
(2,611
)
 

 
 
 
 
 
 
 
 
 
 
 
 
(a) 
Amounts are recorded to interest charges.
(b) 
Amounts are recorded to electric operating revenues. Portions of these gains and losses are subject to sharing with electric customers through margin-sharing mechanisms and deducted from gross revenue as appropriate.
(c) 
Certain derivatives are utilized to mitigate natural gas price risk for electric generation and are recorded to electric fuel and purchased power, subject to cost-recovery mechanisms and reclassified to a regulatory asset, as appropriate. Amounts for the three months ended March 31, 2018 and 2017 included $1.2 million of settlement losses and $0.9 million of settlement gains, respectively. The remaining derivative settlement gains and losses for the three months ended March 31, 2018 and 2017 relate to natural gas operations and are recorded to cost of natural gas sold and transported. These gains and losses are subject to cost-recovery mechanisms and reclassified out of income to a regulatory asset or liability, as appropriate.

PSCo had no derivative instruments designated as fair value hedges during the three months ended March 31, 2018 and 2017. Therefore, no gains or losses from fair value hedges or related hedged transactions were recognized for these periods.

Consideration of Credit Risk and Concentrations — PSCo continuously monitors the creditworthiness of the counterparties to its interest rate derivatives and commodity derivative contracts prior to settlement, and assesses each counterparty’s ability to perform on the transactions set forth in the contracts. Given this assessment, as well as an assessment of the impact of PSCo’s own credit risk when determining the fair value of derivative liabilities, the impact of credit risk was immaterial to the fair value of unsettled commodity derivatives presented in the consolidated balance sheets.

PSCo employs additional credit risk control mechanisms when appropriate, such as letters of credit, parental guarantees, standardized master netting agreements and termination provisions that allow for offsetting of positive and negative exposures. Credit exposure is monitored and, when necessary, the activity with a specific counterparty is limited until credit enhancement is provided.

PSCo’s most significant concentrations of credit risk with particular entities or industries are contracts with counterparties to its wholesale, trading and non-trading commodity activities. At March 31, 2018, four of PSCo’s 10 most significant counterparties for these activities, comprising $9.8 million or 14 percent of this credit exposure, had investment grade credit ratings from Standard & Poor’s, Moody’s or Fitch Ratings. Five of the 10 most significant counterparties, comprising $22.4 million or 31 percent of this credit exposure, were not rated by these external agencies, but based on PSCo’s internal analysis, had credit quality consistent with investment grade. The one remaining significant counterparty, comprising $21.2 million or 29 percent of this credit exposure, had credit quality less than investment grade, based on ratings from external analysis. Nine of these significant counterparties are municipal or cooperative electric entities, or other utilities.

Credit Related Contingent Features — Contract provisions for derivative instruments that PSCo enters into, including those accounted for as normal purchase-normal sale contracts and therefore not reflected on the balance sheet, may require the posting of collateral or settlement of the contracts for various reasons, including if PSCo’s credit ratings are downgraded below its investment grade credit rating by any of the major credit rating agencies or for cross-default contractual provisions that could result in the settlement of such contracts if there was a failure under other financing arrangements related to payment terms or other covenants. At March 31, 2018 and Dec. 31, 2017, there were no derivative instruments in a material liability position with such underlying contract provisions.

Certain derivative instruments are also subject to contract provisions that contain adequate assurance clauses. These provisions allow counterparties to seek performance assurance, including cash collateral, in the event that PSCo’s ability to fulfill its contractual obligations is reasonably expected to be impaired. PSCo had no collateral posted related to adequate assurance clauses in derivative contracts as of March 31, 2018 and Dec. 31, 2017.

Recurring Fair Value Measurements — The following table presents, for each of the fair value hierarchy levels, PSCo’s assets and liabilities measured at fair value on a recurring basis at March 31, 2018:
 
 
March 31, 2018
 
 
Fair Value
 
Fair Value
Total
 
Counterparty
Netting (b)
 
 
(Thousands of Dollars)
 
Level 1
 
Level 2
 
Level 3
 
 
 
Total
Current derivative assets
 
 
 
 
 
 
 
 
 
 
 
 
Other derivative instruments:
 
 
 
 
 
 
 
 
 
 
 
 
Commodity trading
 
$
587

 
$
7,965

 
$
2

 
$
8,554

 
$
(5,373
)
 
$
3,181

Total current derivative assets
 
$
587

 
$
7,965

 
$
2

 
$
8,554

 
$
(5,373
)
 
3,181

PPAs (a)
 
 
 
 
 
 
 
 
 
 
 
1,716

Current derivative instruments
 
 
 
 
 
 
 
 
 
 
 
$
4,897

Noncurrent derivative assets
 
 
 
 
 
 
 
 
 
 
 
 
Other derivative instruments:
 
 
 
 
 
 
 
 
 
 
 
 
Commodity trading
 
$
—

 
$
2,298

 
$
—

 
$
2,298

 
$
(1,236
)
 
$
1,062

Total noncurrent derivative assets
 
$
—

 
$
2,298

 
$
—

 
$
2,298

 
$
(1,236
)
 
1,062

PPAs (a)
 
 
 
 
 
 
 
 
 
 
 
31

Noncurrent derivative instruments
 
 
 
 
 
 
 
 
 
 
 
$
1,093

Current derivative liabilities
 
 
 
 
 
 
 
 
 
 
 
 
Other derivative instruments:
 
 
 
 
 
 
 
 
 
 
 
 
Commodity trading
 
$
457

 
$
7,528

 
$
1

 
$
7,986

 
$
(5,372
)
 
$
2,614

Total current derivative liabilities
 
$
457

 
$
7,528

 
$
1

 
$
7,986

 
$
(5,372
)
 
2,614

PPAs (a)
 
 
 
 
 
 
 
 
 
 
 
4,730

Current derivative instruments
 
 
 
 
 
 
 
 
 
 
 
$
7,344

Noncurrent derivative liabilities
 
 
 
 
 
 
 
 
 
 
 
 
Other derivative instruments:
 
 
 
 
 
 
 
 
 
 
 
 
Commodity trading
 
$
—

 
$
2,224

 
$
—

 
$
2,224

 
$
(1,236
)
 
$
988

Total noncurrent derivative liabilities
 
$
—

 
$
2,224

 
$
—

 
$
2,224

 
$
(1,236
)
 
988

PPAs (a)
 
 
 
 
 
 
 
 
 
 
 
1,379

Noncurrent derivative instruments
 
 
 
 
 
 
 
 
 
 
 
$
2,367


(a) 
During 2006, PSCo qualified these contracts under the normal purchase exception. Based on this qualification, the contracts are no longer adjusted to fair value and the previous carrying value of these contracts will be amortized over the remaining contract lives along with the offsetting regulatory assets and liabilities.
(b) 
PSCo nets derivative instruments and related collateral in its consolidated balance sheet when supported by a legally enforceable master netting agreement, and all derivative instruments and related collateral amounts were subject to master netting agreements at March 31, 2018. At March 31, 2018, derivative assets and liabilities include no obligations to return cash collateral or rights to reclaim cash collateral. The counterparty netting amounts presented exclude settlement receivables and payables and non-derivative amounts that may be subject to the same master netting agreements.

The following table presents, for each of the fair value hierarchy levels, PSCo’s assets and liabilities measured at fair value on a recurring basis at Dec. 31, 2017:
 
 
Dec. 31, 2017
 
 
Fair Value
 
Fair Value
Total
 
Counterparty
Netting (b)
 
 
(Thousands of Dollars)
 
Level 1
 
Level 2
 
Level 3
 
 
 
Total
Current derivative assets
 
 
 
 
 
 
 
 
 
 
 
 
Other derivative instruments:
 
 
 
 
 
 
 
 
 
 
 
 
Commodity trading
 
$
528

 
$
4,488

 
$
12

 
$
5,028

 
$
(3,554
)
 
$
1,474

Natural gas commodity
 
—

 
18

 
—

 
18

 
(10
)
 
8

Total current derivative assets
 
$
528

 
$
4,506

 
$
12

 
$
5,046

 
$
(3,564
)
 
1,482

                                                         
 
 
 
 
 
 
 
 
 
 
 
1,715

Current derivative instruments
 
 
 
 
 
 
 
 
 
 
 
$
3,197

Noncurrent derivative assets
 
 
 
 
 
 
 
 
 
 
 
 
Other derivative instruments:
 
 
 
 

 
 
 
 

 
 

 
 

Commodity trading
 
$
—

 
$
1,541

 
$
—

 
$
1,541

 
$
(563
)
 
$
978

Total noncurrent derivative assets
 
$
—

 
$
1,541

 
$
—

 
$
1,541

 
$
(563
)
 
978

PPAs (a)
 
 
 
 
 
 
 
 
 
 
 
31

Noncurrent derivative instruments
 
 
 
 
 
 
 
 
 
 
 
$
1,009

Current derivative liabilities
 
 
 
 
 
 
 
 
 
 
 
 
Other derivative instruments:
 
 
 
 
 
 
 
 
 
 
 
 
Commodity trading
 
$
446

 
$
4,285

 
$
6

 
$
4,737

 
$
(3,431
)
 
$
1,306

Natural gas commodity
 
—

 
1,016

 
—

 
1,016

 
(10
)
 
1,006

Total current derivative liabilities
 
$
446

 
$
5,301

 
$
6

 
$
5,753

 
$
(3,441
)
 
2,312

PPAs (a)
 
 
 
 
 
 
 
 
 
 
 
5,036

Current derivative instruments
 
 
 
 
 
 
 
 
 
 
 
$
7,348

Noncurrent derivative liabilities
 
 
 
 
 
 
 
 
 
 
 
 
Other derivative instruments:
 
 

 
 

 
 

 
 

 
 

 
 

Commodity trading
 
$
—

 
$
1,362

 
$
—

 
$
1,362

 
$
(563
)
 
$
799

Total noncurrent derivative liabilities
 
$
—

 
$
1,362

 
$
—

 
$
1,362

 
$
(563
)
 
799

PPAs (a)
 
 
 
 
 
 
 
 
 
 
 
$
2,669

Noncurrent derivative instruments
 
 
 
 
 
 
 
 
 
 
 
$
3,468


(a) 
During 2006, PSCo qualified these contracts under the normal purchase exception. Based on this qualification, the contracts are no longer adjusted to fair value and the previous carrying value of these contracts will be amortized over the remaining contract lives along with the offsetting regulatory assets and liabilities.
(b) 
PSCo nets derivative instruments and related collateral in its consolidated balance sheet when supported by a legally enforceable master netting agreement, and all derivative instruments and related collateral amounts were subject to master netting agreements at Dec. 31, 2017. At Dec. 31, 2017, derivative assets and liabilities include no obligations to return cash collateral or rights to reclaim cash collateral. The counterparty netting amounts presented exclude settlement receivables and payables and non-derivative amounts that may be subject to the same master netting agreements.

There were immaterial gains and losses recognized in earnings for Level 3 commodity trading derivatives in the three months ended March 31, 2018 and 2017.

PSCo recognizes transfers between levels as of the beginning of each period. There were no transfers of amounts between levels for derivative instruments for the three months ended March 31, 2018 and 2017.

Fair Value of Long-Term Debt

As of March 31, 2018 and Dec. 31, 2017, other financial instruments for which the carrying amount did not equal fair value were as follows:
 
 
March 31, 2018
 
Dec. 31, 2017
(Thousands of Dollars)
 
Carrying
Amount
 
Fair Value
 
Carrying
Amount
 
Fair Value
Long-term debt, including current portion
 
$
4,607,825

 
$
4,845,116

 
$
4,608,275

 
$
5,024,840



The fair value of PSCo’s long-term debt is estimated based on recent trades and observable spreads from benchmark interest rates for similar securities. The fair value estimates are based on information available to management as of March 31, 2018 and Dec. 31, 2017, and given the observability of the inputs to these estimates, the fair values presented for long-term debt have been assigned a Level 2.
v3.8.0.1
Other Income, Net
 3 Months Ended
Mar. 31, 2018
Other Income and Expenses [Abstract]  
Other Income, Net
Other Income, Net

Other income, net consisted of the following:
 
 
Three Months Ended March 31
 
(Thousands of Dollars)
 
2018
 
2017
 
Other nonoperating income
 
$
482

 
$
3,431

 
Interest (expense) income
 
(136
)
 
375

 
Insurance policy expense
 
(77
)
 
(79
)
 
Benefits non-service cost
 
(29
)
 
(513
)
 
Other nonoperating expense
 
(9
)
 
(10
)
 
Other income, net
 
$
231

 
$
3,204

 
v3.8.0.1
Segment Information
 3 Months Ended
Mar. 31, 2018
Segment Reporting [Abstract]  
Segment Information
Segment Information

Operating results from the regulated electric utility and regulated natural gas utility are each separately and regularly reviewed by PSCo’s chief operating decision maker. PSCo evaluates performance based on profit or loss generated from the product or service provided. These segments are managed separately because the revenue streams are dependent upon regulated rate recovery, which is separately determined for each segment.

PSCo has the following reportable segments: regulated electric utility, regulated natural gas utility and all other.

•
PSCo’s regulated electric utility segment generates, transmits and distributes electricity primarily in portions of Colorado. In addition, this segment includes sales for resale and provides wholesale transmission service to various entities in the United States. Regulated electric utility also includes PSCo’s commodity trading operations.
•
PSCo’s regulated natural gas utility segment transports, stores and distributes natural gas primarily in portions of Colorado.
•
Revenues from operating segments not included above are below the necessary quantitative thresholds and are therefore included in the all other category. Those primarily include steam revenue, appliance repair services and nonutility real estate activities.

Asset and capital expenditure information is not provided for PSCo’s reportable segments because as an integrated electric and natural gas utility, PSCo operates significant assets that are not dedicated to a specific business segment, and reporting assets and capital expenditures by business segment would require arbitrary and potentially misleading allocations which may not necessarily reflect the assets that would be required for the operation of the business segments on a stand-alone basis.

To report income from operations for regulated electric and regulated natural gas utility segments, the majority of costs are directly assigned to each segment. However, some costs, such as common depreciation, common O&M expenses and interest expense are allocated based on cost causation allocators. A general allocator is used for certain general and administrative expenses, including office supplies, rent, property insurance and general advertising.
(Thousands of Dollars)
 
Regulated Electric
 
Regulated Natural Gas
 
All Other
 
Reconciling Eliminations
 
Consolidated Total
Three Months Ended March 31, 2018
 
 
 
 
 
 
 
 
 
 
Operating revenues (a)(b)
 
$
698,274

 
$
363,986

 
$
11,038

 
$
—

 
$
1,073,298

Intersegment revenues
 
112

 
64

 
—

 
(176
)
 
—

Total revenues
 
$
698,386

 
$
364,050

 
$
11,038

 
$
(176
)
 
$
1,073,298

Net income
 
$
79,551

 
$
53,712

 
$
459

 
$
—

 
$
133,722


(Thousands of Dollars)
 
Regulated Electric
 
Regulated Natural Gas
 
All Other
 
Reconciling Eliminations
 
Consolidated Total
Three Months Ended March 31, 2017
 
 
 
 
 
 
 
 
 
 
Operating revenues (a)(b)
 
$
711,388

 
$
356,136

 
$
13,010

 
$
—

 
$
1,080,534

Intersegment revenues
 
92

 
56

 
—

 
(148
)
 
—

Total revenues
 
$
711,480

 
$
356,192

 
$
13,010

 
$
(148
)
 
$
1,080,534

Net income (loss)
 
$
76,144

 
$
34,483

 
$
919

 
$
—

 
$
111,546


(a)    Operating revenues include $1 million and $2 million of affiliate electric revenue for the three months ended March 31, 2018 and 2017.
(b)    Operating revenues include $1 million of other affiliate revenue for the three months ended March 31, 2018 and 2017.
v3.8.0.1
Benefit Plans and Other Postretirement Benefits
 3 Months Ended
Mar. 31, 2018
Retirement Benefits [Abstract]  
Benefit Plans and Other Postretirement Benefits
Benefit Plans and Other Postretirement Benefits

Components of Net Periodic Benefit Cost (Credit)
 
 
 
 
 
 
 
 
 
 
 
Three Months Ended March 31
 
 
2018
 
2017
 
2018
 
2017
(Thousands of Dollars)
 
Pension Benefits
 
Postretirement Health
Care Benefits
Service cost
 
$
7,271

 
$
6,820

 
$
152

 
$
192

Interest cost (a)
 
11,814

 
12,640

 
3,749

 
4,191

Expected return on plan assets (a)
 
(17,130
)
 
(17,134
)
 
(5,675
)
 
(5,476
)
Amortization of prior service credit (a)
 
(845
)
 
(803
)
 
(1,545
)
 
(1,562
)
Amortization of net loss (a)
 
7,815

 
7,089

 
1,021

 
961

Net periodic benefit cost (credit)
 
8,925

 
8,612

 
(2,298
)
 
(1,694
)
Credits not recognized due to the effects of regulation
 
1,475

 
736

 
—

 
—

Net benefit cost (credit) recognized for financial reporting
 
$
10,400

 
$
9,348

 
$
(2,298
)
 
$
(1,694
)


(a)
The components of net periodic cost other than the service cost component are included in the line item “other income, net” in the income statement or capitalized on the balance sheet as a regulatory asset.

In January 2018, contributions of $150.0 million were made across four of Xcel Energy’s pension plans, of which $22.0 million was attributable to PSCo. Xcel Energy does not expect additional pension contributions during 2018.
v3.8.0.1
Other Comprehensive Income
 3 Months Ended
Mar. 31, 2018
Stockholders' Equity Note [Abstract]  
Other Comprehensive Income
Other Comprehensive Income (Loss)

Changes in accumulated other comprehensive loss, net of tax, for the three months ended March 31, 2018 and 2017 were as follows:
 
 
Three Months Ended March 31, 2018
(Thousands of Dollars)
 
Gains and Losses on Cash Flow Hedges
 
Defined Benefit and Postretirement Items
 
Total
Accumulated other comprehensive loss at Jan. 1
 
$
(26,465
)
 
$
(267
)
 
$
(26,732
)
Losses reclassified from net accumulated other comprehensive loss
 
300

 
2

 
302

Net current period other comprehensive income
 
300

 
2

 
302

Accumulated other comprehensive loss at March 31
 
$
(26,165
)
 
$
(265
)
 
$
(26,430
)
 
 
Three Months Ended March 31, 2017
(Thousands of Dollars)
 
Gains and Losses on Cash Flow Hedges
 
Defined Benefit and Postretirement Items
 
Total
Accumulated other comprehensive loss at Jan. 1
 
$
(22,780
)
 
$
(220
)
 
$
(23,000
)
Losses reclassified from net accumulated other comprehensive loss
 
246

 
1

 
247

Net current period other comprehensive income
 
246

 
1

 
247

Accumulated other comprehensive loss at March 31
 
$
(22,534
)
 
$
(219
)
 
$
(22,753
)

Reclassifications from accumulated other comprehensive loss for the three months ended March 31, 2018 and 2017 were as follows:
 
 
 
 
 
 
 
 
Amounts Reclassified from Accumulated Other
Comprehensive Loss
 
(Thousands of Dollars)
 
Three Months Ended March 31, 2018
 
Three Months Ended March 31, 2017
 
Losses on cash flow hedges:
 
 

 
 
 
Interest rate derivatives
 
$
398

(a) 
$
398

(a) 
Total, pre-tax
 
398

 
398

 
Tax benefit
 
(98
)
 
(152
)
 
Total, net of tax
 
300

 
246

 
Defined benefit pension and postretirement losses:
 
 
 
 
 
Amortization of net loss
 
2

(b) 
2

(b) 
Total, pre-tax
 
2

 
2

 
Tax benefit
 
—

 
(1
)
 
Total, net of tax
 
2

 
1

 
Total amounts reclassified, net of tax
 
$
302

 
$
247

 
 
 
 
 
 
 
(a) 
Included in interest charges.
(b) 
Included in the computation of net periodic pension and postretirement benefit costs. See Note 11 for details regarding these benefit plans.
v3.8.0.1
Revenues
 3 Months Ended
Mar. 31, 2018
Revenue from Contract with Customer [Abstract]  
Revenue from Contract with Customer [Text Block]
Revenues

PSCo principally generates revenue from the transmission, distribution and sale of electricity and the transportation, distribution and sale of natural gas to wholesale and retail customers. Performance obligations related to the sale of energy are satisfied as energy is delivered to customers. PSCo recognizes revenue in an amount that corresponds directly to the price of the energy delivered to the customer. The measurement of energy sales to customers is generally based on the reading of their meters, which occurs on a systematic basis throughout the month. At the end of each month, amounts of energy delivered to customers since the date of the last meter reading are estimated, and the corresponding unbilled revenue is recognized. Contract terms are generally short-term in nature, and as such PSCo does not recognize a separate financing component of its collections from customers. PSCo presents its revenues net of any excise or other fiduciary-type taxes or fees.

PSCo has various rate-adjustment mechanisms in place that provide for the recovery of natural gas, electric fuel and purchased energy costs. These cost-adjustment tariffs may increase or decrease the level of revenue collected from customers and are revised periodically for differences between the total amount collected under the clauses and the costs incurred. When applicable, under governing regulatory commission rate orders, fuel cost over-recoveries (the excess of fuel revenue billed to customers over fuel costs incurred) are deferred as regulatory liabilities and under-recoveries (the excess of fuel costs incurred over fuel revenues billed to customers) are deferred as regulatory assets.

Certain rate rider mechanisms qualify as alternative revenue programs under GAAP. These mechanisms arise from costs imposed upon the utility by action of a regulator or legislative body related to an environmental, public safety or other mandate. When certain criteria are met (including collection within 24 months), revenue is recognized equal to the revenue requirement, which may include return on rate base items and incentives. The mechanisms are revised periodically for differences between the total amount collected and the revenue recognized, which may increase or decrease the level of revenue collected from customers. Alternative revenue is recorded on a gross basis and is disclosed separate from revenue from contracts with customers in the period earned.

In the following tables, revenue is classified by the type of goods/services rendered and market/customer type. The tables also reconcile revenue to the reportable segments.
 
 
Three Months Ended March 31, 2018
(Thousands of Dollars)
 
Regulated Electric
 
Regulated Natural Gas
 
All Other
 
Total
Major revenue types
 
 
 
 
 
 
 
 
Revenue from contracts with customers:
 
 
 
 
 
 
 
 
Residential
 
$
227,649

 
$
227,746

 
$
2,696

 
$
458,091

Commercial and industrial (C&I)
 
343,226

 
86,028

 
7,159

 
436,413

Other
 
12,176

 
—

 
60

 
12,236

Total retail
 
583,051

 
313,774

 
9,915

 
906,740

Wholesale
 
47,890

 
—

 
—

 
47,890

Transmission
 
12,252

 
—

 
—

 
12,252

Other
 
18,831

 
24,929

 
—

 
43,760

Total revenue from contracts with customers
 
662,024

 
338,703

 
9,915

 
1,010,642

Alternative revenue and other
 
36,250

 
25,283

 
1,123

 
62,656

Total revenues
 
$
698,274

 
$
363,986

 
$
11,038

 
$
1,073,298


 
 
Three Months Ended March 31, 2017
(Thousands of Dollars)
 
Regulated Electric
 
Regulated Natural Gas
 
All Other
 
Total
Major revenue types
 
 
 
 
 
 
 
 
Revenue from contracts with customers:
 
 
 
 
 
 
 
 
Residential
 
$
234,434

 
$
225,910

 
$
2,564

 
$
462,908

C&I
 
359,697

 
86,242

 
9,260

 
455,199

Other
 
12,675

 
—

 
63

 
12,738

Total retail
 
606,806

 
312,152

 
11,887

 
930,845

Wholesale
 
43,576

 
—

 
—

 
43,576

Transmission
 
14,639

 
—

 
—

 
14,639

Other
 
16,695

 
22,610

 
—

 
39,305

Total revenue from contracts with customers
 
681,716

 
334,762

 
11,887

 
1,028,365

Alternative revenue and other
 
29,672

 
21,374

 
1,123

 
52,169

Total revenues
 
$
711,388

 
$
356,136

 
$
13,010

 
$
1,080,534
v3.8.0.1
Selected Balance Sheet Data (Tables)
 3 Months Ended
Mar. 31, 2018
Balance Sheet Related Disclosures [Abstract]  
Accounts Receivable, Net
(Thousands of Dollars)
 
March 31, 2018
 
Dec. 31, 2017
Accounts receivable, net
 
 
 
 
Accounts receivable
 
$
332,506

 
$
314,009

Less allowance for bad debts
 
(19,980
)
 
(19,606
)
 
 
$
312,526

 
$
294,403
Inventories
(Thousands of Dollars)
 
March 31, 2018
 
Dec. 31, 2017
Inventories
 
 
 
 
Materials and supplies
 
$
69,378

 
$
68,940

Fuel
 
53,282

 
73,893

Natural gas
 
31,266

 
71,656

 
 
$
153,926

 
$
214,489
Property, Plant and Equipment, Net
(Thousands of Dollars)
 
March 31, 2018
 
Dec. 31, 2017
Property, plant and equipment, net
 
 
 
 
Electric plant
 
$
12,692,880

 
$
12,627,592

Natural gas plant
 
4,140,582

 
4,102,075

Common and other property
 
1,031,570

 
1,022,333

Plant to be retired (a)
 
10,627

 
10,949

Construction work in progress
 
1,264,835

 
1,014,338

Total property, plant and equipment
 
19,140,494

 
18,777,287

Less accumulated depreciation
 
(4,849,019
)
 
(4,751,536
)
 
 
$
14,291,475

 
$
14,025,751



(a) 
In the third quarter of 2017, PSCo early retired Valmont Unit 5 and converted Cherokee Unit 4 from a coal-fueled generating facility to natural gas. PSCo also expects Craig Unit 1 to be early retired in approximately 2025. Amounts are presented net of accumulated depreciation.
v3.8.0.1
Income Taxes (Tables)
 3 Months Ended
Mar. 31, 2018
Income Tax Disclosure [Abstract]  
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]
Total income tax expense from operations differs from the amount computed by applying the statutory federal income tax rate to income before income tax expense. The following reconciles such differences:
 
Three Months ended March 31
 
 
2018
 
2017
Federal statutory rate
 
21.0
 %
 
35.0
 %
State tax, net of federal tax effect
 
3.7

 
3.0

Increases (decreases) in tax from:
 
 
 
 
Regulatory differences - ARAM (a)
(3.3
)
 
(0.1
)
Regulatory differences - ARAM deferral (b)
3.1

 
—

Regulatory differences - other utility plant items
(1.3
)
 
(0.4
)
Other tax credits, net of federal income tax expense
(1.0
)
 
(0.7
)
Other, net
0.4

 
0.1

Effective income tax rate
 
22.6
 %
 
36.9
 %

(a)  
The average rate assumption method (ARAM); a method to flow back excess deferred taxes to customers.
(b)
As we receive further clarity or direction from our commissions regarding the flow back to customers of excess deferred taxes resulting from the TCJA, the ARAM deferral may decrease during the year, which would result in a reduction to tax expense with a correlating reduction to revenue.
Summary of Statute of Limitations Applicable to Open Tax Years [Table Text Block]
PSCO is a member of the Xcel Energy affiliated group that files a consolidated federal income tax return. The statute of limitations applicable to Xcel Energy’s federal income tax returns expire as follows:
Tax Year(s)
 
Expiration
2009 - 2011
 
December 2018
2012 - 2013
 
October 2018
2014
 
September 2018
2015
 
September 2019
2016
 
September 2020
Reconciliation of Unrecognized Tax Benefits
reconciliation of the amount of unrecognized tax benefit is as follows:
(Millions of Dollars)
 
March 31, 2018
 
Dec. 31, 2017
Unrecognized tax benefit — Permanent tax positions
 
$
4.1

 
$
4.0

Unrecognized tax benefit — Temporary tax positions
 
6.0

 
6.1

Total unrecognized tax benefit
 
$
10.1

 
$
10.1
Tax Benefits Associated with NOL and Tax Credit Carryforwards
he unrecognized tax benefit amounts were reduced by the tax benefits associated with NOL and tax credit carryforwards. The amounts of tax benefits associated with NOL and tax credit carryforwards are as follows:
(Millions of Dollars)
 
March 31, 2018
 
Dec. 31, 2017
NOL and tax credit carryforwards
 
$
(4.2
)
 
$
(4.0
)
v3.8.0.1
Rate Matters (Tables)
 3 Months Ended
Mar. 31, 2018
Public Utilities, General Disclosures [Abstract]  
Colorado 2017 Multi-Year Electric Rate Case [Table Text Block]
Revenue Request (Millions of Dollars)
 
2018
 
2019
 
2020
 
2021
 
Total
Revenue request
 
$
74

 
$
75

 
$
60

 
$
36

 
$
245

Clean Air Clean Jobs Act (CACJA) rider conversion to base rates
 
90

 
—

 
—

 
—

 
90

Transmission Cost Adjustment (TCA) rider conversion to base rates
 
43

 
—

 
—

 
—

 
43

  Total
 
$
207

 
$
75

 
$
60

 
$
36

 
$
378

 
 
 
 
 
 
 
 
 
 
 
Expected year-end rate base (billions of dollars)
 
$
6.8

 
$
7.1

 
$
7.3

 
$
7.4

 
 
Colorado 2017 Multi-Year Gas Rate Case [Table Text Block]
The request, detailed below, is based on FTYs, a 10.0 percent ROE and an equity ratio of 55.25 percent.
Revenue Request (Millions of Dollars)
 
2018
 
2019
 
2020
 
Total
Revenue request
 
$
63

 
$
33

 
$
43

 
$
139

Pipeline System Integrity Adjustment (PSIA) rider conversion to base rates (a)
 
—

 
94

 
—

 
94

Total
 
$
63

 
$
127

 
$
43

 
$
233

 
 
 
 
 
 
 
 
 
Expected year-end rate base (billions of dollars) (b)
 
$
1.5

 
$
2.3

 
$
2.4

 
 
 
(a)  
The roll-in of PSIA rider revenue into base rates will not have an impact on customer bills or revenue as these costs are already being recovered through the rider. The recovery of incremental PSIA related investments in 2019 and 2020 are included in the base rate request.
(b)  
The additional rate base in 2019 predominantly reflects the roll-in of capital associated with the PSIA rider.
v3.8.0.1
Borrowings and Other Financing Instruments (Tables)
 3 Months Ended
Mar. 31, 2018
Borrowings and Other Financing Instruments [Abstract]  
Credit Facilities
At March 31, 2018, PSCo had the following committed credit facility available (in millions of dollars):
Credit Facility (a)
 
Drawn (b)
 
Available
$
700

 
$
99

 
$
601


(a)    This credit facility expires in June 2021.
(b)    Includes outstanding commercial paper and letters of credit.
Money Pool  
Borrowings and Other Financing Instruments [Abstract]  
Short-Term Borrowings
Money pool borrowings for PSCo were as follows:
(Amounts in Millions, Except Interest Rates)
 
Three Months Ended March 31, 2018
 
Year Ended Dec. 31, 2017
Borrowing limit
 
$
250

 
$
250

Amount outstanding at period end
 
48

 
—

Average amount outstanding
 
12

 
—

Maximum amount outstanding
 
97

 
20

Weighted average interest rate, computed on a daily basis
 
1.64
%
 
0.92
%
Weighted average interest rate at period end
 
1.64

 
N/A
Commercial Paper  
Borrowings and Other Financing Instruments [Abstract]  
Short-Term Borrowings
Commercial paper outstanding for PSCo was as follows:
(Amounts in Millions, Except Interest Rates)
 
Three Months Ended March 31, 2018
 
Year Ended Dec. 31, 2017
Borrowing limit
 
$
700

 
$
700

Amount outstanding at period end
 
95

 
—

Average amount outstanding
 
50

 
54

Maximum amount outstanding
 
151

 
268

Weighted average interest rate, computed on a daily basis
 
1.82
%
 
1.08
%
Weighted average interest rate at period end
 
2.28

 
N/A
v3.8.0.1
Fair Value of Financial Assets and Liabilities (Tables)
 3 Months Ended
Mar. 31, 2018
Fair Value Disclosures [Abstract]  
Gross Notional Amounts of Commodity Forwards and Options
The following table details the gross notional amounts of commodity forwards and options at March 31, 2018 and Dec. 31, 2017:
(Amounts in Thousands) (a)(b)
 
March 31, 2018
 
Dec. 31, 2017
Megawatt hours of electricity
 
21,657

 
22,260

Million British thermal units of natural gas
 
11,780

 
13,410


(a) 
Amounts are not reflective of net positions in the underlying commodities.
(b) 
Notional amounts for options are included on a gross basis, but are weighted for the probability of exercise.
Impact of Derivative Activity on Accumulated Other Comprehensive Loss, Regulatory Assets and Liabilities, and Income
The following tables detail the impact of derivative activity during the three months ended March 31, 2018 and 2017 on accumulated other comprehensive loss, regulatory assets and liabilities, and income:
 
 
Three Months Ended March 31, 2018
 
 
 
Pre-Tax Fair Value
Losses Recognized
During the Period in:
 
Pre-Tax Losses
Reclassified into Income
During the Period from:
 
 
 
(Thousands of Dollars)
 
Accumulated
Other
Comprehensive
Loss
 
Regulatory
(Assets) and
Liabilities
 
Accumulated
Other
Comprehensive
Loss
 
Regulatory
Assets and
(Liabilities)
 
Pre-Tax Gains (Losses)
Recognized
During the Period
in Income
 
Derivatives designated as cash flow hedges
 
 
 
 
 
 
 
 
 
 
 
Interest rate
 
$
—

 
$
—

 
$
398

(a) 
$
—

 
$
—

 
Total
 
$
—

 
$
—

 
$
398

 
$
—

 
$
—

 
Other derivative instruments
 
 
 
 
 
 
 
 
 
 
 
Commodity trading
 
$
—

 
$
—

 
$
—

 
$
—

 
$
524

(b) 
Natural gas commodity
 
—

 
(171
)
 
—

 
2,749

(c) 
(1,581
)
(c) 
Total
 
$
—

 
$
(171
)
 
$
—

 
$
2,749

 
$
(1,057
)
 
 
 
 
 
 
 
 
 
 
 
 
 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
Three Months Ended March 31, 2017
 
 
 
Pre-Tax Fair Value
Losses Recognized
During the Period in:
 
Pre-Tax Losses
Reclassified into Income
During the Period from:
 
 
 
(Thousands of Dollars)
 
Accumulated
Other
Comprehensive
Loss
 
Regulatory
(Assets) and
Liabilities
 
Accumulated
Other
Comprehensive
Loss
 
Regulatory
Assets and
(Liabilities)
 
Pre-Tax Gains (Losses)
Recognized
During the Period
in Income
 
Derivatives designated as cash flow hedges
 
 
 
 
 
 
 
 
 
 
 
Interest rate
 
$
—

 
$
—

 
$
398

(a) 
$
—

 
$
—

 
Total
 
$
—

 
$
—

 
$
398

 
$
—

 
$
—

 
Other derivative instruments
 
 
 
 
 
 
 
 
 
 
 
Commodity trading
 
$
—

 
$
—

 
$
—

 
$
—

 
$
379

(b) 
Natural gas commodity
 
—

 
(5,387
)
 
—

 
282

(c) 
(2,990
)
(c) 
Total
 
$
—

 
$
(5,387
)
 
$
—

 
$
282

 
$
(2,611
)
 

 
 
 
 
 
 
 
 
 
 
 
 
(a) 
Amounts are recorded to interest charges.
(b) 
Amounts are recorded to electric operating revenues. Portions of these gains and losses are subject to sharing with electric customers through margin-sharing mechanisms and deducted from gross revenue as appropriate.
(c) 
Certain derivatives are utilized to mitigate natural gas price risk for electric generation and are recorded to electric fuel and purchased power, subject to cost-recovery mechanisms and reclassified to a regulatory asset, as appropriate. Amounts for the three months ended March 31, 2018 and 2017 included $1.2 million of settlement losses and $0.9 million of settlement gains, respectively. The remaining derivative settlement gains and losses for the three months ended March 31, 2018 and 2017 relate to natural gas operations and are recorded to cost of natural gas sold and transported. These gains and losses are subject to cost-recovery mechanisms and reclassified out of income to a regulatory asset or liability, as appropriate.
Derivative Assets and Liabilities Measured at Fair Value on a Recurring Basis by Hierarchy Level
Recurring Fair Value Measurements — The following table presents, for each of the fair value hierarchy levels, PSCo’s assets and liabilities measured at fair value on a recurring basis at March 31, 2018:
 
 
March 31, 2018
 
 
Fair Value
 
Fair Value
Total
 
Counterparty
Netting (b)
 
 
(Thousands of Dollars)
 
Level 1
 
Level 2
 
Level 3
 
 
 
Total
Current derivative assets
 
 
 
 
 
 
 
 
 
 
 
 
Other derivative instruments:
 
 
 
 
 
 
 
 
 
 
 
 
Commodity trading
 
$
587

 
$
7,965

 
$
2

 
$
8,554

 
$
(5,373
)
 
$
3,181

Total current derivative assets
 
$
587

 
$
7,965

 
$
2

 
$
8,554

 
$
(5,373
)
 
3,181

PPAs (a)
 
 
 
 
 
 
 
 
 
 
 
1,716

Current derivative instruments
 
 
 
 
 
 
 
 
 
 
 
$
4,897

Noncurrent derivative assets
 
 
 
 
 
 
 
 
 
 
 
 
Other derivative instruments:
 
 
 
 
 
 
 
 
 
 
 
 
Commodity trading
 
$
—

 
$
2,298

 
$
—

 
$
2,298

 
$
(1,236
)
 
$
1,062

Total noncurrent derivative assets
 
$
—

 
$
2,298

 
$
—

 
$
2,298

 
$
(1,236
)
 
1,062

PPAs (a)
 
 
 
 
 
 
 
 
 
 
 
31

Noncurrent derivative instruments
 
 
 
 
 
 
 
 
 
 
 
$
1,093

Current derivative liabilities
 
 
 
 
 
 
 
 
 
 
 
 
Other derivative instruments:
 
 
 
 
 
 
 
 
 
 
 
 
Commodity trading
 
$
457

 
$
7,528

 
$
1

 
$
7,986

 
$
(5,372
)
 
$
2,614

Total current derivative liabilities
 
$
457

 
$
7,528

 
$
1

 
$
7,986

 
$
(5,372
)
 
2,614

PPAs (a)
 
 
 
 
 
 
 
 
 
 
 
4,730

Current derivative instruments
 
 
 
 
 
 
 
 
 
 
 
$
7,344

Noncurrent derivative liabilities
 
 
 
 
 
 
 
 
 
 
 
 
Other derivative instruments:
 
 
 
 
 
 
 
 
 
 
 
 
Commodity trading
 
$
—

 
$
2,224

 
$
—

 
$
2,224

 
$
(1,236
)
 
$
988

Total noncurrent derivative liabilities
 
$
—

 
$
2,224

 
$
—

 
$
2,224

 
$
(1,236
)
 
988

PPAs (a)
 
 
 
 
 
 
 
 
 
 
 
1,379

Noncurrent derivative instruments
 
 
 
 
 
 
 
 
 
 
 
$
2,367


(a) 
During 2006, PSCo qualified these contracts under the normal purchase exception. Based on this qualification, the contracts are no longer adjusted to fair value and the previous carrying value of these contracts will be amortized over the remaining contract lives along with the offsetting regulatory assets and liabilities.
(b) 
PSCo nets derivative instruments and related collateral in its consolidated balance sheet when supported by a legally enforceable master netting agreement, and all derivative instruments and related collateral amounts were subject to master netting agreements at March 31, 2018. At March 31, 2018, derivative assets and liabilities include no obligations to return cash collateral or rights to reclaim cash collateral. The counterparty netting amounts presented exclude settlement receivables and payables and non-derivative amounts that may be subject to the same master netting agreements.

The following table presents, for each of the fair value hierarchy levels, PSCo’s assets and liabilities measured at fair value on a recurring basis at Dec. 31, 2017:
 
 
Dec. 31, 2017
 
 
Fair Value
 
Fair Value
Total
 
Counterparty
Netting (b)
 
 
(Thousands of Dollars)
 
Level 1
 
Level 2
 
Level 3
 
 
 
Total
Current derivative assets
 
 
 
 
 
 
 
 
 
 
 
 
Other derivative instruments:
 
 
 
 
 
 
 
 
 
 
 
 
Commodity trading
 
$
528

 
$
4,488

 
$
12

 
$
5,028

 
$
(3,554
)
 
$
1,474

Natural gas commodity
 
—

 
18

 
—

 
18

 
(10
)
 
8

Total current derivative assets
 
$
528

 
$
4,506

 
$
12

 
$
5,046

 
$
(3,564
)
 
1,482

                                                         
 
 
 
 
 
 
 
 
 
 
 
1,715

Current derivative instruments
 
 
 
 
 
 
 
 
 
 
 
$
3,197

Noncurrent derivative assets
 
 
 
 
 
 
 
 
 
 
 
 
Other derivative instruments:
 
 
 
 

 
 
 
 

 
 

 
 

Commodity trading
 
$
—

 
$
1,541

 
$
—

 
$
1,541

 
$
(563
)
 
$
978

Total noncurrent derivative assets
 
$
—

 
$
1,541

 
$
—

 
$
1,541

 
$
(563
)
 
978

PPAs (a)
 
 
 
 
 
 
 
 
 
 
 
31

Noncurrent derivative instruments
 
 
 
 
 
 
 
 
 
 
 
$
1,009

Current derivative liabilities
 
 
 
 
 
 
 
 
 
 
 
 
Other derivative instruments:
 
 
 
 
 
 
 
 
 
 
 
 
Commodity trading
 
$
446

 
$
4,285

 
$
6

 
$
4,737

 
$
(3,431
)
 
$
1,306

Natural gas commodity
 
—

 
1,016

 
—

 
1,016

 
(10
)
 
1,006

Total current derivative liabilities
 
$
446

 
$
5,301

 
$
6

 
$
5,753

 
$
(3,441
)
 
2,312

PPAs (a)
 
 
 
 
 
 
 
 
 
 
 
5,036

Current derivative instruments
 
 
 
 
 
 
 
 
 
 
 
$
7,348

Noncurrent derivative liabilities
 
 
 
 
 
 
 
 
 
 
 
 
Other derivative instruments:
 
 

 
 

 
 

 
 

 
 

 
 

Commodity trading
 
$
—

 
$
1,362

 
$
—

 
$
1,362

 
$
(563
)
 
$
799

Total noncurrent derivative liabilities
 
$
—

 
$
1,362

 
$
—

 
$
1,362

 
$
(563
)
 
799

PPAs (a)
 
 
 
 
 
 
 
 
 
 
 
$
2,669

Noncurrent derivative instruments
 
 
 
 
 
 
 
 
 
 
 
$
3,468


(a) 
During 2006, PSCo qualified these contracts under the normal purchase exception. Based on this qualification, the contracts are no longer adjusted to fair value and the previous carrying value of these contracts will be amortized over the remaining contract lives along with the offsetting regulatory assets and liabilities.
(b) 
PSCo nets derivative instruments and related collateral in its consolidated balance sheet when supported by a legally enforceable master netting agreement, and all derivative instruments and related collateral amounts were subject to master netting agreements at Dec. 31, 2017. At Dec. 31, 2017, derivative assets and liabilities include no obligations to return cash collateral or rights to reclaim cash collateral. The counterparty netting amounts presented exclude settlement receivables and payables and non-derivative amounts that may be subject to the same master netting agreements.
Carrying Amount and Fair Value of Long-term Debt
As of March 31, 2018 and Dec. 31, 2017, other financial instruments for which the carrying amount did not equal fair value were as follows:
 
 
March 31, 2018
 
Dec. 31, 2017
(Thousands of Dollars)
 
Carrying
Amount
 
Fair Value
 
Carrying
Amount
 
Fair Value
Long-term debt, including current portion
 
$
4,607,825

 
$
4,845,116

 
$
4,608,275

 
$
5,024,840
v3.8.0.1
Other Income, Net (Tables)
 3 Months Ended
Mar. 31, 2018
Other Income and Expenses [Abstract]  
Other Income, Net
Other income, net consisted of the following:
 
 
Three Months Ended March 31
 
(Thousands of Dollars)
 
2018
 
2017
 
Other nonoperating income
 
$
482

 
$
3,431

 
Interest (expense) income
 
(136
)
 
375

 
Insurance policy expense
 
(77
)
 
(79
)
 
Benefits non-service cost
 
(29
)
 
(513
)
 
Other nonoperating expense
 
(9
)
 
(10
)
 
Other income, net
 
$
231

 
$
3,204

 
v3.8.0.1
Segment Information (Tables)
 3 Months Ended
Mar. 31, 2018
Segment Reporting [Abstract]  
Results from Operations by Reportable Segment
(Thousands of Dollars)
 
Regulated Electric
 
Regulated Natural Gas
 
All Other
 
Reconciling Eliminations
 
Consolidated Total
Three Months Ended March 31, 2018
 
 
 
 
 
 
 
 
 
 
Operating revenues (a)(b)
 
$
698,274

 
$
363,986

 
$
11,038

 
$
—

 
$
1,073,298

Intersegment revenues
 
112

 
64

 
—

 
(176
)
 
—

Total revenues
 
$
698,386

 
$
364,050

 
$
11,038

 
$
(176
)
 
$
1,073,298

Net income
 
$
79,551

 
$
53,712

 
$
459

 
$
—

 
$
133,722


(Thousands of Dollars)
 
Regulated Electric
 
Regulated Natural Gas
 
All Other
 
Reconciling Eliminations
 
Consolidated Total
Three Months Ended March 31, 2017
 
 
 
 
 
 
 
 
 
 
Operating revenues (a)(b)
 
$
711,388

 
$
356,136

 
$
13,010

 
$
—

 
$
1,080,534

Intersegment revenues
 
92

 
56

 
—

 
(148
)
 
—

Total revenues
 
$
711,480

 
$
356,192

 
$
13,010

 
$
(148
)
 
$
1,080,534

Net income (loss)
 
$
76,144

 
$
34,483

 
$
919

 
$
—

 
$
111,546


(a)    Operating revenues include $1 million and $2 million of affiliate electric revenue for the three months ended March 31, 2018 and 2017.
(b)    Operating revenues include $1 million of other affiliate revenue for the three months ended March 31, 2018 and 2017.
v3.8.0.1
Benefit Plans and Other Postretirement Benefits (Tables)
 3 Months Ended
Mar. 31, 2018
Retirement Benefits [Abstract]  
Components of Net Periodic Benefit Cost (Credit)
Components of Net Periodic Benefit Cost (Credit)
 
 
 
 
 
 
 
 
 
 
 
Three Months Ended March 31
 
 
2018
 
2017
 
2018
 
2017
(Thousands of Dollars)
 
Pension Benefits
 
Postretirement Health
Care Benefits
Service cost
 
$
7,271

 
$
6,820

 
$
152

 
$
192

Interest cost (a)
 
11,814

 
12,640

 
3,749

 
4,191

Expected return on plan assets (a)
 
(17,130
)
 
(17,134
)
 
(5,675
)
 
(5,476
)
Amortization of prior service credit (a)
 
(845
)
 
(803
)
 
(1,545
)
 
(1,562
)
Amortization of net loss (a)
 
7,815

 
7,089

 
1,021

 
961

Net periodic benefit cost (credit)
 
8,925

 
8,612

 
(2,298
)
 
(1,694
)
Credits not recognized due to the effects of regulation
 
1,475

 
736

 
—

 
—

Net benefit cost (credit) recognized for financial reporting
 
$
10,400

 
$
9,348

 
$
(2,298
)
 
$
(1,694
)
v3.8.0.1
Other Comprehensive Income (Tables)
 3 Months Ended
Mar. 31, 2018
Stockholders' Equity Note [Abstract]  
Changes in Accumulated Other Comprehensive Loss, Net of Tax
Changes in accumulated other comprehensive loss, net of tax, for the three months ended March 31, 2018 and 2017 were as follows:
 
 
Three Months Ended March 31, 2018
(Thousands of Dollars)
 
Gains and Losses on Cash Flow Hedges
 
Defined Benefit and Postretirement Items
 
Total
Accumulated other comprehensive loss at Jan. 1
 
$
(26,465
)
 
$
(267
)
 
$
(26,732
)
Losses reclassified from net accumulated other comprehensive loss
 
300

 
2

 
302

Net current period other comprehensive income
 
300

 
2

 
302

Accumulated other comprehensive loss at March 31
 
$
(26,165
)
 
$
(265
)
 
$
(26,430
)
 
 
Three Months Ended March 31, 2017
(Thousands of Dollars)
 
Gains and Losses on Cash Flow Hedges
 
Defined Benefit and Postretirement Items
 
Total
Accumulated other comprehensive loss at Jan. 1
 
$
(22,780
)
 
$
(220
)
 
$
(23,000
)
Losses reclassified from net accumulated other comprehensive loss
 
246

 
1

 
247

Net current period other comprehensive income
 
246

 
1

 
247

Accumulated other comprehensive loss at March 31
 
$
(22,534
)
 
$
(219
)
 
$
(22,753
)
Reclassifications out of Accumulated Other Comprehensive Loss
Reclassifications from accumulated other comprehensive loss for the three months ended March 31, 2018 and 2017 were as follows:
 
 
 
 
 
 
 
 
Amounts Reclassified from Accumulated Other
Comprehensive Loss
 
(Thousands of Dollars)
 
Three Months Ended March 31, 2018
 
Three Months Ended March 31, 2017
 
Losses on cash flow hedges:
 
 

 
 
 
Interest rate derivatives
 
$
398

(a) 
$
398

(a) 
Total, pre-tax
 
398

 
398

 
Tax benefit
 
(98
)
 
(152
)
 
Total, net of tax
 
300

 
246

 
Defined benefit pension and postretirement losses:
 
 
 
 
 
Amortization of net loss
 
2

(b) 
2

(b) 
Total, pre-tax
 
2

 
2

 
Tax benefit
 
—

 
(1
)
 
Total, net of tax
 
2

 
1

 
Total amounts reclassified, net of tax
 
$
302

 
$
247

 
 
 
 
 
 
 
(a) 
Included in interest charges.
(b) 
v3.8.0.1
Revenues (Tables)
 3 Months Ended
Mar. 31, 2018
Revenue from Contract with Customer [Abstract]  
Disaggregation of Revenue [Table Text Block]
 
 
Three Months Ended March 31, 2018
(Thousands of Dollars)
 
Regulated Electric
 
Regulated Natural Gas
 
All Other
 
Total
Major revenue types
 
 
 
 
 
 
 
 
Revenue from contracts with customers:
 
 
 
 
 
 
 
 
Residential
 
$
227,649

 
$
227,746

 
$
2,696

 
$
458,091

Commercial and industrial (C&I)
 
343,226

 
86,028

 
7,159

 
436,413

Other
 
12,176

 
—

 
60

 
12,236

Total retail
 
583,051

 
313,774

 
9,915

 
906,740

Wholesale
 
47,890

 
—

 
—

 
47,890

Transmission
 
12,252

 
—

 
—

 
12,252

Other
 
18,831

 
24,929

 
—

 
43,760

Total revenue from contracts with customers
 
662,024

 
338,703

 
9,915

 
1,010,642

Alternative revenue and other
 
36,250

 
25,283

 
1,123

 
62,656

Total revenues
 
$
698,274

 
$
363,986

 
$
11,038

 
$
1,073,298


 
 
Three Months Ended March 31, 2017
(Thousands of Dollars)
 
Regulated Electric
 
Regulated Natural Gas
 
All Other
 
Total
Major revenue types
 
 
 
 
 
 
 
 
Revenue from contracts with customers:
 
 
 
 
 
 
 
 
Residential
 
$
234,434

 
$
225,910

 
$
2,564

 
$
462,908

C&I
 
359,697

 
86,242

 
9,260

 
455,199

Other
 
12,675

 
—

 
63

 
12,738

Total retail
 
606,806

 
312,152

 
11,887

 
930,845

Wholesale
 
43,576

 
—

 
—

 
43,576

Transmission
 
14,639

 
—

 
—

 
14,639

Other
 
16,695

 
22,610

 
—

 
39,305

Total revenue from contracts with customers
 
681,716

 
334,762

 
11,887

 
1,028,365

Alternative revenue and other
 
29,672

 
21,374

 
1,123

 
52,169

Total revenues
 
$
711,388

 
$
356,136

 
$
13,010

 
$
1,080,534
v3.8.0.1
Accounting Pronouncements (Details) - Accounting Standards Update 2017-07
$ in Millions
 3 Months Ended
Mar. 31, 2017
USD ($)
Operating and Maintenance Expense  
New Accounting Pronouncements or Change in Accounting Principle [Line Items]  
Net benefit cost (credit) recognized for financial reporting $ (0.5)
Other Income  
New Accounting Pronouncements or Change in Accounting Principle [Line Items]  
Net benefit cost (credit) recognized for financial reporting $ 0.5
v3.8.0.1
Selected Balance Sheet Data (Details) - USD ($)
$ in Thousands
Mar. 31, 2018
Dec. 31, 2017
Accounts receivable, net    
Accounts receivable $ 332,506 $ 314,009
Less allowance for bad debts (19,980) (19,606)
Accounts receivable, net $ 312,526 $ 294,403
v3.8.0.1
Selected Balance Sheet Data Balance Sheet Related Disclosures, Inventories (Details) - USD ($)
$ in Thousands
Mar. 31, 2018
Dec. 31, 2017
Public Utilities, Inventory [Line Items]    
Inventories $ 153,926 $ 214,489
Materials and supplies    
Public Utilities, Inventory [Line Items]    
Inventories 69,378 68,940
Fuel    
Public Utilities, Inventory [Line Items]    
Inventories 53,282 73,893
Natural gas    
Public Utilities, Inventory [Line Items]    
Inventories $ 31,266 $ 71,656
v3.8.0.1
Selected Balance Sheet Data Balance Sheet Related Disclosures, Property, Plant and Equipment (Details) - USD ($)
$ in Thousands
Mar. 31, 2018
Dec. 31, 2017
Public Utility, Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross $ 19,140,494 $ 18,777,287
Less accumulated depreciation (4,849,019) (4,751,536)
Property, plant and equipment, net 14,291,475 14,025,751
Electric plant    
Public Utility, Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 12,692,880 12,627,592
Natural gas plant    
Public Utility, Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 4,140,582 4,102,075
Common and other property    
Public Utility, Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 1,031,570 1,022,333
Plant to be retired    
Public Utility, Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross [1] 10,627 10,949
Construction work in progress    
Public Utility, Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross $ 1,264,835 $ 1,014,338
[1] (a) In the third quarter of 2017, PSCo early retired Valmont Unit 5 and converted Cherokee Unit 4 from a coal-fueled generating facility to natural gas. PSCo also expects Craig Unit 1 to be early retired in approximately 2025. Amounts are presented net of accumulated depreciation.
v3.8.0.1
Income Taxes (Details) - USD ($)
 3 Months Ended 9 Months Ended 12 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Sep. 30, 2015
Dec. 31, 2012
Dec. 31, 2017
Tax Audits [Abstract]          
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent 21.00% 35.00%      
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent 3.70% 3.00%      
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent (3.30%) (0.10%)      
Effective Income Tax Rate Reconciliation, Tax Cuts and Jobs Act of 2017, Change in Tax Rate, Percent 3.10% 0.00%      
Effective Income Tax Rate Reconciliation, Other Regulatory Items, Percent (1.30%) (0.40%)      
Effective Income Tax Rate Reconciliation Regulatory Differences Utility Plant Items (1.00%) (0.70%)      
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent 0.40% 0.10%      
Effective Income Tax Rate Reconciliation, Percent 22.60% 36.90%      
Unrecognized Tax Benefits [Abstract]          
Unrecognized tax benefit — Permanent tax positions $ 4,100,000       $ 4,000,000
Unrecognized tax benefit — Temporary tax positions 6,000,000       6,100,000
Total unrecognized tax benefit 10,100,000       10,100,000
NOL and tax credit carryforwards (4,200,000)       (4,000,000)
Upper bound of decrease in unrecognized tax benefit that is reasonably possible 6,000,000        
Amounts accrued for penalties related to unrecognized tax benefits $ 0       $ 0
Internal Revenue Service (IRS)          
Tax Audits [Abstract]          
Year(s) under examination     2012 and 2013 2010 and 2011  
Year of carryback claim under examination       2009  
State Jurisdiction (Colorado)          
Tax Audits [Abstract]          
Earliest year subject to examination 2009        
v3.8.0.1
Rate Matters (Details) - USD ($)
$ in Millions
 1 Months Ended 3 Months Ended
Apr. 30, 2018
Feb. 28, 2018
Oct. 31, 2017
Jun. 30, 2017
Mar. 31, 2018
CPUC Proceeding - 2017 Multi-Year Gas Rate Case          
Public Utilities, General Disclosures [Line Items]          
Public Utilities, Number of Years Which Rates are Requested to Increase       3 years  
Public Utilities, Requested Return on Equity, Percentage       10.00%  
Public Utilities, Requested Equity Capital Structure, Percentage       55.25%  
Public Utilities, Requested Rate Increase (Decrease), Amount       $ 139  
Public Utilities, Rate Impact       233  
CPUC Proceeding - 2017 Multi-Year Gas Rate Case, Gas Rates 2018          
Public Utilities, General Disclosures [Line Items]          
Public Utilities, Requested Rate Increase (Decrease), Amount       63  
Public Utilities, Rate Impact       63  
Public Utilities, Expected Year-End Rate Base [1]       1,500  
CPUC Proceeding - 2017 Multi-Year Gas Rate Case, Gas Rates 2019          
Public Utilities, General Disclosures [Line Items]          
Public Utilities, Requested Rate Increase (Decrease), Amount       33  
Public Utilities, Rate Impact       127  
Public Utilities, Expected Year-End Rate Base [1]       2,300  
CPUC Proceeding - 2017 Multi-Year Gas Rate Case, Gas Rates 2020          
Public Utilities, General Disclosures [Line Items]          
Public Utilities, Requested Rate Increase (Decrease), Amount       43  
Public Utilities, Rate Impact       43  
Public Utilities, Expected Year-End Rate Base [1]       2,400  
CPUC Staff | CPUC Proceeding - 2017 Multi-Year Gas Rate Case          
Public Utilities, General Disclosures [Line Items]          
Public Utilities, Recommended Length of Average Rate Base     13 months    
Public Utilities, Recommended Equity Capital Structure, Percentage     48.73%    
Office of Consumer Council (OCC) | CPUC Proceeding - 2017 Multi-Year Gas Rate Case          
Public Utilities, General Disclosures [Line Items]          
Public Utilities, Recommended Length of Average Rate Base     13 months    
Public Utilities, Recommended Equity Capital Structure, Percentage     51.20%    
PSCo | CPUC Proceeding - 2017 Multi-Year Gas Rate Case          
Public Utilities, General Disclosures [Line Items]          
Public Utilities, Reduction of Provisional Rates   $ 20      
Public Utilities, Requested Rate Increase (Decrease), Amount       139  
Public Utilities, Provisional Rates Subject to Refund         $ 63
PSCo | CPUC Proceeding - Colorado 2017 Multi-Year Electric Rate Case          
Public Utilities, General Disclosures [Line Items]          
Public Utilities, Approximate Rate Increase (Decrease), Amount     $ 245    
Public Utilities, Number of Years Which Rates are Requested to Increase     4 years    
Public Utilities, Requested Return on Equity, Percentage     10.00%    
Public Utilities, Requested Equity Capital Structure, Percentage     55.25%    
Public Utilities, Requested Rate Increase (Decrease), Amount     $ 245    
Public Utilities, Rate Impact     378    
PSCo | CPUC Proceeding - 2017 Multi-Year Electric Rate Case, Electric Rates 2018          
Public Utilities, General Disclosures [Line Items]          
Public Utilities, Requested Rate Increase (Decrease), Amount     74    
Public Utilities, Rate Impact     207    
Public Utilities, Expected Year-End Rate Base     6,800    
PSCo | CPUC Proceeding - 2017 Multi-Year Electric Rate Case, Electric Rates 2019          
Public Utilities, General Disclosures [Line Items]          
Public Utilities, Requested Rate Increase (Decrease), Amount     75    
Public Utilities, Rate Impact     75    
Public Utilities, Expected Year-End Rate Base     7,100    
PSCo | CPUC Proceeding - 2017 Multi-Year Electric Rate Case, Electric Rates 2020          
Public Utilities, General Disclosures [Line Items]          
Public Utilities, Requested Rate Increase (Decrease), Amount     60    
Public Utilities, Rate Impact     60    
Public Utilities, Expected Year-End Rate Base     7,300    
PSCo | CPUC Proceeding - 2017 Multi-Year Electric Rate Case, Electric Rates 2021          
Public Utilities, General Disclosures [Line Items]          
Public Utilities, Requested Rate Increase (Decrease), Amount     36    
Public Utilities, Rate Impact     36    
Public Utilities, Expected Year-End Rate Base     7,400    
PSCo | CPUC Staff | CPUC Proceeding - 2017 Multi-Year Gas Rate Case, Gas Rates 2018          
Public Utilities, General Disclosures [Line Items]          
Public Utilities, Total Recommended Rate Increase (Decrease)     30    
PSCo | Office of Consumer Council (OCC) | CPUC Proceeding - 2017 Multi-Year Gas Rate Case, Gas Rates 2018          
Public Utilities, General Disclosures [Line Items]          
Public Utilities, Total Recommended Rate Increase (Decrease)     39    
Subsequent Event | PSCo | CPUC Proceeding - Tax Cuts and Jobs Act of 2017 [Member]          
Public Utilities, General Disclosures [Line Items]          
Tax Cuts and Jobs Act of 2017, 2018 Electric Rate Reduction Under Settlement $ 101        
Subsequent Event | PSCo | Colorado Public Utilities Commission [Member] | CPUC Proceeding - Tax Cuts and Jobs Act of 2017 [Member]          
Public Utilities, General Disclosures [Line Items]          
Tax Cuts and Jobs Act of 2017, 2018 Electric Refund of TCJA Benefits Under Settlement 42        
Tax Cuts and Jobs Act of 2017, Amount of Accelerated Prepaid Pension Asset Amortization Under Settlement $ 59        
Clean Air Clean Jobs Act (CACJA) Recovery Rider | CPUC Proceeding - Colorado 2017 Multi-Year Electric Rate Case          
Public Utilities, General Disclosures [Line Items]          
Public Utilities, Rider Conversion to Base Rates     90    
Clean Air Clean Jobs Act (CACJA) Recovery Rider | CPUC Proceeding - 2017 Multi-Year Electric Rate Case, Electric Rates 2018          
Public Utilities, General Disclosures [Line Items]          
Public Utilities, Rider Conversion to Base Rates     90    
Clean Air Clean Jobs Act (CACJA) Recovery Rider | CPUC Proceeding - 2017 Multi-Year Electric Rate Case, Electric Rates 2019          
Public Utilities, General Disclosures [Line Items]          
Public Utilities, Rider Conversion to Base Rates     0    
Clean Air Clean Jobs Act (CACJA) Recovery Rider | CPUC Proceeding - 2017 Multi-Year Electric Rate Case, Electric Rates 2020          
Public Utilities, General Disclosures [Line Items]          
Public Utilities, Rider Conversion to Base Rates     0    
Clean Air Clean Jobs Act (CACJA) Recovery Rider | CPUC Proceeding - 2017 Multi-Year Electric Rate Case, Electric Rates 2021          
Public Utilities, General Disclosures [Line Items]          
Public Utilities, Rider Conversion to Base Rates     0    
Transmission Cost Adjustment (TCA) Rider | CPUC Proceeding - Colorado 2017 Multi-Year Electric Rate Case          
Public Utilities, General Disclosures [Line Items]          
Public Utilities, Rider Conversion to Base Rates     43    
Transmission Cost Adjustment (TCA) Rider | CPUC Proceeding - 2017 Multi-Year Electric Rate Case, Electric Rates 2018          
Public Utilities, General Disclosures [Line Items]          
Public Utilities, Rider Conversion to Base Rates     43    
Transmission Cost Adjustment (TCA) Rider | CPUC Proceeding - 2017 Multi-Year Electric Rate Case, Electric Rates 2019          
Public Utilities, General Disclosures [Line Items]          
Public Utilities, Rider Conversion to Base Rates     0    
Transmission Cost Adjustment (TCA) Rider | CPUC Proceeding - 2017 Multi-Year Electric Rate Case, Electric Rates 2020          
Public Utilities, General Disclosures [Line Items]          
Public Utilities, Rider Conversion to Base Rates     0    
Transmission Cost Adjustment (TCA) Rider | CPUC Proceeding - 2017 Multi-Year Electric Rate Case, Electric Rates 2021          
Public Utilities, General Disclosures [Line Items]          
Public Utilities, Rider Conversion to Base Rates     $ 0    
Pipeline System Integrity Adjustment (PSIA) Rider | CPUC Proceeding - 2017 Multi-Year Gas Rate Case          
Public Utilities, General Disclosures [Line Items]          
Public Utilities, Rider Conversion to Base Rates [2]       94  
Pipeline System Integrity Adjustment (PSIA) Rider | CPUC Proceeding - 2017 Multi-Year Gas Rate Case, Gas Rates 2018          
Public Utilities, General Disclosures [Line Items]          
Public Utilities, Rider Conversion to Base Rates [2]       0  
Pipeline System Integrity Adjustment (PSIA) Rider | CPUC Proceeding - 2017 Multi-Year Gas Rate Case, Gas Rates 2019          
Public Utilities, General Disclosures [Line Items]          
Public Utilities, Rider Conversion to Base Rates [2]       94  
Pipeline System Integrity Adjustment (PSIA) Rider | CPUC Proceeding - 2017 Multi-Year Gas Rate Case, Gas Rates 2020          
Public Utilities, General Disclosures [Line Items]          
Public Utilities, Rider Conversion to Base Rates [2]       $ 0  
[1] The additional rate base in 2019 predominantly reflects the roll-in of capital associated with the PSIA rider.
[2] The roll-in of PSIA rider revenue into base rates will not have an impact on customer bills or revenue as these costs are already being recovered through the rider. The recovery of incremental PSIA related investments in 2019 and 2020 are included in the base rate request.
v3.8.0.1
Commitments and Contingencies, Purchased Power Agreements (Details) - Independent Power Producing Entities - MW
 3 Months Ended
Mar. 31, 2018
Dec. 31, 2017
Purchased Power Agreements [Abstract]    
Generating capacity under long term purchased power agreements (in MW) 1,571 1,571
Purchase Power Agreement Expiration (year) 2032  
v3.8.0.1
Commitments and Contingencies, Environmental Contingencies (Details) - Other MGP, Landfill, or Disposal Sites [Domain]
$ in Millions
Mar. 31, 2018
USD ($)
Site
Unrecorded Unconditional Purchase Obligation [Line Items]  
Number of identified MGP sites under current investigation and/or remediation | Site 2
Accrual for Environmental Loss Contingencies, Gross | $ $ 1
v3.8.0.1
Commitments and Contingencies, Legal Contingencies (Details)
 1 Months Ended
Dec. 31, 2015
PSCo | Minimum [Member] | Line Extension Disputes  
Legal Contingencies [Abstract]  
Loss Contingency, Number of Plaintiffs 50
v3.8.0.1
Borrowings and Other Financing Instruments, Short-Term Borrowings (Details) - USD ($)
 3 Months Ended 12 Months Ended
Mar. 31, 2018
Dec. 31, 2017
Short-term Debt [Line Items]    
Amount outstanding at period end $ 95,000,000 $ 0
Money Pool    
Short-term Debt [Line Items]    
Borrowing limit 250,000,000 250,000,000
Amount outstanding at period end 48,000,000 0
Average amount outstanding 12,000,000 0
Maximum amount outstanding $ 97,000,000 $ 20,000,000
Weighted average interest rate, computed on a daily basis (percentage) 1.64% 0.92%
Weighted average interest rate at period end (percentage) 1.64%  
Commercial Paper    
Short-term Debt [Line Items]    
Borrowing limit $ 700,000,000 $ 700,000,000
Amount outstanding at period end 95,000,000 0
Average amount outstanding 50,000,000 54,000,000
Maximum amount outstanding $ 151,000,000 $ 268,000,000
Weighted average interest rate, computed on a daily basis (percentage) 1.82% 1.08%
Weighted average interest rate at period end (percentage) 2.28%  
v3.8.0.1
Borrowings and Other Financing Instruments, Letters of Credit (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2018
Dec. 31, 2017
Line of Credit Facility [Line Items]    
Amount outstanding at period end $ 95,000 $ 0
Letter of Credit    
Line of Credit Facility [Line Items]    
Amount outstanding at period end $ 4,000 $ 3,000
Letter of Credit | Letter of Credit    
Line of Credit Facility [Line Items]    
Term of letters of credit (in years) 1 year  
v3.8.0.1
Borrowings and Other Financing Instruments, Credit Facility (Details) - Credit Facility - USD ($)
 3 Months Ended
Mar. 31, 2018
Dec. 31, 2017
Line of Credit Facility [Line Items]    
Credit Facility [1] $ 700,000,000  
Drawn [2] 99,000,000  
Available $ 601,000,000  
Maturity Date Jun. 30, 2021  
Direct advances on the credit facility outstanding $ 0 $ 0
[1] This credit facility expires in June 2021.
[2] Includes outstanding commercial paper and letters of credit.
v3.8.0.1
Fair Value of Financial Assets and Liabilities, Derivative Instruments (Details)
MWh in Thousands, MMBTU in Thousands, $ in Millions
Mar. 31, 2018
USD ($)
MMBTU
MWh
Counterparty
Dec. 31, 2017
MMBTU
MWh
Credit Concentration Risk    
Consideration of Credit Risk and Concentrations [Abstract]    
Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure | Counterparty 10  
Credit Concentration Risk | Municipal or Cooperative Entities or Other Utilities [Member]    
Consideration of Credit Risk and Concentrations [Abstract]    
Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure 9  
Credit Concentration Risk | External Credit Rating, Investment Grade [Member]    
Consideration of Credit Risk and Concentrations [Abstract]    
Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure 4  
Wholesale, trading and non-trading commodity credit exposure for the most significant counterparties $ 9.8  
Percentage of wholesale, trading and non-trading commodity credit exposure for the most significant counterparties (in hundredths) 14.00%  
Credit Concentration Risk | No Investment Grade Ratings from External Credit Rating Agencies [Member]    
Consideration of Credit Risk and Concentrations [Abstract]    
Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure 5  
Wholesale, trading and non-trading commodity credit exposure for the most significant counterparties $ 22.4  
Percentage of wholesale, trading and non-trading commodity credit exposure for the most significant counterparties (in hundredths) 31.00%  
Credit Concentration Risk | Credit Quality Less Than Investment Grade [Member]    
Consideration of Credit Risk and Concentrations [Abstract]    
Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure 1  
Wholesale, trading and non-trading commodity credit exposure for the most significant counterparties $ 21.2  
Percentage of wholesale, trading and non-trading commodity credit exposure for the most significant counterparties (in hundredths) 29.00%  
Interest Rate Swap    
Interest Rate Derivatives [Abstract]    
Amount of accumulated other comprehensive gains (losses) related to interest rate derivatives expected to be reclassified into earnings within the next twelve months $ (1.2)  
Electric Commodity (in megawatt hours)    
Gross Notional Amounts of Commodity Forwards and Options [Abstract]    
Derivative, Nonmonetary Notional amount | MWh [1],[2] 21,657 22,260
Natural Gas Commodity (in million British thermal units)    
Gross Notional Amounts of Commodity Forwards and Options [Abstract]    
Derivative, Nonmonetary Notional amount | MMBTU [1],[2] 11,780 13,410
[1] Amounts are not reflective of net positions in the underlying commodities.
[2] Notional amounts for options are included on a gross basis, but are weighted for the probability of exercise.
v3.8.0.1
Fair Value of Financial Assets and Liabilities, Impact of Derivative Activity (Details) - USD ($)
 3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Financial Impact of Qualifying Fair Value Hedges on Earnings [Abstract]    
Derivative instruments designated as fair value hedges $ 0 $ 0
Recognized gains (losses) from fair value hedges or related hedged transactions 0 0
Designated as Hedging Instrument | Cash Flow Hedges    
Impact of Derivative Activity on Accumulated Other Comprehensive Loss, Regulatory Assets and Liabilities, and Income [Abstract]    
Pre-tax fair value gains (losses) recognized during the period in accumulated other comprehensive loss 0 0
Pre-tax fair value gains (losses) recognized during the period in regulatory (assets) and liabilities 0 0
Pre-tax (gains) losses reclassified into income during the period from accumulated other comprehensive loss 398,000 398,000
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities) 0 0
Pre-tax gains (losses) recognized during the period in income 0 0
Designated as Hedging Instrument | Cash Flow Hedges | Interest Rate    
Impact of Derivative Activity on Accumulated Other Comprehensive Loss, Regulatory Assets and Liabilities, and Income [Abstract]    
Pre-tax fair value gains (losses) recognized during the period in accumulated other comprehensive loss 0 0
Pre-tax fair value gains (losses) recognized during the period in regulatory (assets) and liabilities 0 0
Pre-tax (gains) losses reclassified into income during the period from accumulated other comprehensive loss [1] 398,000 398,000
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities) 0 0
Pre-tax gains (losses) recognized during the period in income 0 0
Other Derivative Instruments    
Impact of Derivative Activity on Accumulated Other Comprehensive Loss, Regulatory Assets and Liabilities, and Income [Abstract]    
Pre-tax fair value gains (losses) recognized during the period in accumulated other comprehensive loss 0 0
Pre-tax fair value gains (losses) recognized during the period in regulatory (assets) and liabilities (171,000) (5,387,000)
Pre-tax (gains) losses reclassified into income during the period from accumulated other comprehensive loss 0 0
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities) 2,749,000 282,000
Pre-tax gains (losses) recognized during the period in income (1,057,000) (2,611,000)
Other Derivative Instruments | Commodity Trading    
Impact of Derivative Activity on Accumulated Other Comprehensive Loss, Regulatory Assets and Liabilities, and Income [Abstract]    
Pre-tax fair value gains (losses) recognized during the period in accumulated other comprehensive loss 0 0
Pre-tax fair value gains (losses) recognized during the period in regulatory (assets) and liabilities 0 0
Pre-tax (gains) losses reclassified into income during the period from accumulated other comprehensive loss 0 0
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities) 0 0
Pre-tax gains (losses) recognized during the period in income [2] 524,000 379,000
Other Derivative Instruments | Natural Gas Commodity    
Impact of Derivative Activity on Accumulated Other Comprehensive Loss, Regulatory Assets and Liabilities, and Income [Abstract]    
Pre-tax fair value gains (losses) recognized during the period in accumulated other comprehensive loss 0 0
Pre-tax fair value gains (losses) recognized during the period in regulatory (assets) and liabilities (171,000) (5,387,000)
Pre-tax (gains) losses reclassified into income during the period from accumulated other comprehensive loss 0 0
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities) 2,749,000 282,000
Pre-tax gains (losses) recognized during the period in income (1,581,000) (2,990,000) [3]
Other Derivative Instruments | Natural Gas Commodity for Electric Generation    
Impact of Derivative Activity on Accumulated Other Comprehensive Loss, Regulatory Assets and Liabilities, and Income [Abstract]    
Pre-tax fair value gains (losses) recognized during the period in regulatory (assets) and liabilities $ (1,200,000) $ 900,000
[1] Amounts are recorded to interest charges.
[2] {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmI1ZDMwYTAwNWM2ZTRmNDBhODA5NmVjZmUxYmI5MzM1fFRleHRTZWxlY3Rpb246NEE4N0VDMjYzODA2NTRFNkIzN0I3NkVENzdEMDI2MkQM}
[3] {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmI1ZDMwYTAwNWM2ZTRmNDBhODA5NmVjZmUxYmI5MzM1fFRleHRTZWxlY3Rpb246NTBENDc1MThGQ0RBNTBFMEE0NzUwQjYzQUUxNzdBNjQM}
v3.8.0.1
Fair Value of Financial Assets and Liabilities, Credit Related Contingent Features (Details) - USD ($)
Mar. 31, 2018
Dec. 31, 2017
Fair Value Disclosures [Abstract]    
Derivative instruments in a gross liability position $ 0 $ 0
Collateral posted on derivative instruments 0 0
Collateral posted related to adequate assurance clauses in derivative contracts $ 0 $ 0
v3.8.0.1
Fair Value of Financial Assets and Liabilities, Derivative Assets and Liabilities at Fair Value (Details) - USD ($)
$ in Thousands
Mar. 31, 2018
Dec. 31, 2017
Derivatives, Fair Value [Line Items]    
Derivative Asset, Collateral, Obligation to Return Cash, Offset $ 0 $ 0
Derivative Liability, Collateral, Right to Reclaim Cash, Offset 0 0
Other Current Assets    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 4,897 3,197
Other Noncurrent Assets    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 1,093 1,009
Other Current Liabilities    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 7,344 7,348
Other Noncurrent Liabilities    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 2,367 3,468
Fair Value Measured on a Recurring Basis | Other Current Assets    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 3,181 1,482
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset (5,373) [1] (3,564) [2]
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 3,181 1,474
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset (5,373) [1] (3,554) [2]
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Natural Gas Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset   8
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset [2]   (10)
Fair Value Measured on a Recurring Basis | Other Noncurrent Assets    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 1,062 978
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset (1,236) [1] (563) [2]
Fair Value Measured on a Recurring Basis | Other Noncurrent Assets | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 1,062 978
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset [1] (1,236) (563)
Fair Value Measured on a Recurring Basis | Other Current Liabilities    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 2,614 2,312
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset (5,372) [1] (3,441) [2]
Fair Value Measured on a Recurring Basis | Other Current Liabilities | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 2,614 1,306
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset (5,372) [1] (3,431) [2]
Fair Value Measured on a Recurring Basis | Other Current Liabilities | Other Derivative Instruments | Natural Gas Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability   1,006
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset [2]   (10)
Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 988 799
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset (1,236) [1] (563) [2]
Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 988 799
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset (1,236) [1] (563) [2]
Fair Value Measured on a Recurring Basis | Level 1 | Other Current Assets    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 587 528
Fair Value Measured on a Recurring Basis | Level 1 | Other Current Assets | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 587 528
Fair Value Measured on a Recurring Basis | Level 1 | Other Current Assets | Other Derivative Instruments | Natural Gas Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset   0
Fair Value Measured on a Recurring Basis | Level 1 | Other Noncurrent Assets    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 0 0
Fair Value Measured on a Recurring Basis | Level 1 | Other Noncurrent Assets | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 0 0
Fair Value Measured on a Recurring Basis | Level 1 | Other Current Liabilities    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 457 446
Fair Value Measured on a Recurring Basis | Level 1 | Other Current Liabilities | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 457 446
Fair Value Measured on a Recurring Basis | Level 1 | Other Current Liabilities | Other Derivative Instruments | Natural Gas Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability   0
Fair Value Measured on a Recurring Basis | Level 1 | Other Noncurrent Liabilities    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 0 0
Fair Value Measured on a Recurring Basis | Level 1 | Other Noncurrent Liabilities | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 0 0
Fair Value Measured on a Recurring Basis | Level 2 | Other Current Assets    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 7,965 4,506
Fair Value Measured on a Recurring Basis | Level 2 | Other Current Assets | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 7,965 4,488
Fair Value Measured on a Recurring Basis | Level 2 | Other Current Assets | Other Derivative Instruments | Natural Gas Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset   18
Fair Value Measured on a Recurring Basis | Level 2 | Other Noncurrent Assets    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 2,298 1,541
Fair Value Measured on a Recurring Basis | Level 2 | Other Noncurrent Assets | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 2,298 1,541
Fair Value Measured on a Recurring Basis | Level 2 | Other Current Liabilities    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 7,528 5,301
Fair Value Measured on a Recurring Basis | Level 2 | Other Current Liabilities | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 7,528 4,285
Fair Value Measured on a Recurring Basis | Level 2 | Other Current Liabilities | Other Derivative Instruments | Natural Gas Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability   1,016
Fair Value Measured on a Recurring Basis | Level 2 | Other Noncurrent Liabilities    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 2,224 1,362
Fair Value Measured on a Recurring Basis | Level 2 | Other Noncurrent Liabilities | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 2,224 1,362
Fair Value Measured on a Recurring Basis | Level 3 | Other Current Assets    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 2 12
Fair Value Measured on a Recurring Basis | Level 3 | Other Current Assets | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 2 12
Fair Value Measured on a Recurring Basis | Level 3 | Other Current Assets | Other Derivative Instruments | Natural Gas Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset   0
Fair Value Measured on a Recurring Basis | Level 3 | Other Noncurrent Assets    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 0 0
Fair Value Measured on a Recurring Basis | Level 3 | Other Noncurrent Assets | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 0 0
Fair Value Measured on a Recurring Basis | Level 3 | Other Current Liabilities    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 1 6
Fair Value Measured on a Recurring Basis | Level 3 | Other Current Liabilities | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 1 6
Fair Value Measured on a Recurring Basis | Level 3 | Other Current Liabilities | Other Derivative Instruments | Natural Gas Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability   0
Fair Value Measured on a Recurring Basis | Level 3 | Other Noncurrent Liabilities    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 0 0
Fair Value Measured on a Recurring Basis | Level 3 | Other Noncurrent Liabilities | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 0 0
Fair Value, Measurements, Nonrecurring | Other Current Assets | Purchased Power Agreements    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 1,716 [3] 1,715 [4]
Fair Value, Measurements, Nonrecurring | Other Noncurrent Assets | Purchased Power Agreements    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 31 [3] 31 [4]
Fair Value, Measurements, Nonrecurring | Other Current Liabilities | Purchased Power Agreements    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 4,730 [3] 5,036 [4]
Fair Value, Measurements, Nonrecurring | Other Noncurrent Liabilities | Purchased Power Agreements    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 1,379 [3] 2,669 [4]
Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Current Assets    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 8,554 5,046
Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 8,554 5,028
Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Natural Gas Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset   18
Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Noncurrent Assets    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 2,298 1,541
Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Noncurrent Assets | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 2,298 1,541
Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Current Liabilities    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 7,986 5,753
Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Current Liabilities | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 7,986 4,737
Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Current Liabilities | Other Derivative Instruments | Natural Gas Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability   1,016
Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 2,224 1,362
Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability $ 2,224 $ 1,362
[1] PSCo nets derivative instruments and related collateral in its consolidated balance sheet when supported by a legally enforceable master netting agreement, and all derivative instruments and related collateral amounts were subject to master netting agreements at March 31, 2018. At March 31, 2018, derivative assets and liabilities include no obligations to return cash collateral or rights to reclaim cash collateral. The counterparty netting amounts presented exclude settlement receivables and payables and non-derivative amounts that may be subject to the same master netting agreements.
[2] PSCo nets derivative instruments and related collateral in its consolidated balance sheet when supported by a legally enforceable master netting agreement, and all derivative instruments and related collateral amounts were subject to master netting agreements at Dec. 31, 2017. At Dec. 31, 2017, derivative assets and liabilities include no obligations to return cash collateral or rights to reclaim cash collateral. The counterparty netting amounts presented exclude settlement receivables and payables and non-derivative amounts that may be subject to the same master netting agreements.
[3] During 2006, PSCo qualified these contracts under the normal purchase exception. Based on this qualification, the contracts are no longer adjusted to fair value and the previous carrying value of these contracts will be amortized over the remaining contract lives along with the offsetting regulatory assets and liabilities.
[4] During 2006, PSCo qualified these contracts under the normal purchase exception. Based on this qualification, the contracts are no longer adjusted to fair value and the previous carrying value of these contracts will be amortized over the remaining contract lives along with the offsetting regulatory assets and liabilities.
v3.8.0.1
Fair Value of Financial Assets and Liabilities, Changes in Level 3 Commodity Derivatives (Details) - Commodity Contract - USD ($)
 3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Transfers into Level 3 $ 0 $ 0
Transfers out of Level 3 $ 0 $ 0
v3.8.0.1
Fair Value of Financial Assets and Liabilities, Fair Value of Long-Term Debt (Details) - USD ($)
$ in Thousands
Mar. 31, 2018
Dec. 31, 2017
Carrying Amount    
Financial Liabilities, Balance Sheet Groupings [Abstract]    
Long-term debt, including current portion $ 4,607,825 $ 4,608,275
Fair Value    
Financial Liabilities, Balance Sheet Groupings [Abstract]    
Long-term debt, including current portion $ 4,845,116 $ 5,024,840
v3.8.0.1
Other Income, Net (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Other Income and Expenses [Abstract]    
Other Nonoperating Income $ 482 $ 3,431
Interest (expense) income (136) 375
Insurance Policy Expense (Income), Net (77) (79)
Defined Benefit Plan, Non-service Costs (29) (513)
Other Nonoperating Expense (9) (10)
Other income, net $ 231 $ 3,204
v3.8.0.1
Segment Information (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Segment Reporting Information [Line Items]    
Operating revenues $ 1,073,298 $ 1,080,534
Net income 133,722 111,546
Affiliate electric revenue 1,000 2,000
Affiliate other revenue 1,000 1,000
Regulated Electric    
Segment Reporting Information [Line Items]    
Operating revenues 698,386 711,480
Net income 79,551 76,144
Regulated Natural Gas    
Segment Reporting Information [Line Items]    
Operating revenues 364,050 356,192
Net income 53,712 34,483
All Other    
Segment Reporting Information [Line Items]    
Operating revenues 11,038 13,010
Net income 459 919
Operating Segments    
Segment Reporting Information [Line Items]    
Operating revenues [1],[2] 1,073,298 1,080,534
Operating Segments | Regulated Electric    
Segment Reporting Information [Line Items]    
Operating revenues [1] 698,274 711,388
Operating Segments | Regulated Natural Gas    
Segment Reporting Information [Line Items]    
Operating revenues 363,986 356,136
Operating Segments | All Other    
Segment Reporting Information [Line Items]    
Operating revenues [2] 11,038 13,010
Intersegment Eliminations    
Segment Reporting Information [Line Items]    
Operating revenues (176) (148)
Net income 0 0
Intersegment Eliminations | Regulated Electric    
Segment Reporting Information [Line Items]    
Operating revenues 112 92
Intersegment Eliminations | Regulated Natural Gas    
Segment Reporting Information [Line Items]    
Operating revenues 64 56
Intersegment Eliminations | All Other    
Segment Reporting Information [Line Items]    
Operating revenues $ 0 $ 0
[1] Operating revenues include $1 million and $2 million of affiliate electric revenue for the three months ended March 31, 2018 and 2017.
[2] Operating revenues include $1 million of other affiliate revenue for the three months ended March 31, 2018 and 2017.
v3.8.0.1
Benefit Plans and Other Postretirement Benefits (Details)
$ in Thousands
 1 Months Ended 3 Months Ended
Jan. 31, 2018
USD ($)
Plan
Mar. 31, 2018
USD ($)
Mar. 31, 2017
USD ($)
Other Postretirement Benefits Plan [Member]      
Components of Net Periodic Benefit Cost (Credit) [Abstract]      
Service cost   $ 152 $ 192
Interest cost   3,749 4,191
Expected return on plan assets   (5,675) (5,476)
Amortization of prior service credit   (1,545) (1,562)
Amortization of net loss   1,021 961
Net periodic benefit cost (credit)   (2,298) (1,694)
Defined Benefit Plan Credits Not Recognized Due To Effects of Regulation   0 0
Net benefit cost (credit) recognized for financial reporting   (2,298) (1,694)
Pension Plan [Member]      
Components of Net Periodic Benefit Cost (Credit) [Abstract]      
Service cost   7,271 6,820
Interest cost   11,814 12,640
Expected return on plan assets   (17,130) (17,134)
Amortization of prior service credit   (845) (803)
Amortization of net loss   7,815 7,089
Net periodic benefit cost (credit)   8,925 8,612
Defined Benefit Plan Credits Not Recognized Due To Effects of Regulation   1,475 736
Net benefit cost (credit) recognized for financial reporting   $ 10,400 $ 9,348
Total contributions to the pension plans during the period $ 22,000    
Pension Plan [Member] | Xcel Energy Inc.      
Components of Net Periodic Benefit Cost (Credit) [Abstract]      
Total contributions to the pension plans during the period $ 150,000    
Number of Xcel Energy's pension plans to which contributions were made | Plan 4    
v3.8.0.1
Other Comprehensive Income (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]    
Accumulated other comprehensive loss at beginning of period $ 5,828,323  
Losses reclassified from net accumulated other comprehensive loss 302 $ 247
Accumulated other comprehensive loss at end of period 5,866,996  
Gains and Losses on Cash Flow Hedges    
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]    
Accumulated other comprehensive loss at beginning of period (26,465) (22,780)
Losses reclassified from net accumulated other comprehensive loss 300 246
Net current period other comprehensive loss 300 246
Accumulated other comprehensive loss at end of period (26,165) (22,534)
Defined Benefit and Postretirement Items    
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]    
Accumulated other comprehensive loss at beginning of period (267) (220)
Losses reclassified from net accumulated other comprehensive loss 2 1
Net current period other comprehensive loss 2 1
Accumulated other comprehensive loss at end of period (265) (219)
Total    
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]    
Accumulated other comprehensive loss at beginning of period (26,732) (23,000)
Losses reclassified from net accumulated other comprehensive loss 302 247
Net current period other comprehensive loss 302 247
Accumulated other comprehensive loss at end of period $ (26,430) $ (22,753)
v3.8.0.1
Other Comprehensive Income (Reclassification from AOCI) (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]    
Total, pre-tax $ (172,731) $ (176,771)
Tax (benefit) expense 39,009 65,225
Total amounts reclassified, net of tax 302 247
Gains and Losses on Cash Flow Hedges    
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]    
Total amounts reclassified, net of tax 300 246
Gains and Losses on Cash Flow Hedges | Amounts Reclassified from Accumulated Other Comprehensive Loss    
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]    
Total, pre-tax 398 398
Tax (benefit) expense (98) (152)
Total, net of tax 300 246
Gains and Losses on Cash Flow Hedges | Interest Rate Derivatives | Amounts Reclassified from Accumulated Other Comprehensive Loss    
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]    
Interest charges [1] 398 398
Amortizaton of net loss | Amounts Reclassified from Accumulated Other Comprehensive Loss    
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]    
Total, pre-tax [2] 2 2
Defined Benefit and Postretirement Items    
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]    
Total amounts reclassified, net of tax 2 1
Defined Benefit and Postretirement Items | Amounts Reclassified from Accumulated Other Comprehensive Loss    
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]    
Total, pre-tax (2) (2)
Tax benefit 0 (1)
Total amounts reclassified, net of tax $ (2) $ (1)
[1] Included in interest charges.
[2] Included in the computation of net periodic pension and postretirement benefit costs. See Note 11 for details regarding these benefit plans.
v3.8.0.1
Revenues (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Disaggregation of Revenue [Line Items]    
Total revenue from contracts with customers $ 1,010,642 $ 1,028,365
Alternative revenue and other 62,656 52,169
Total operating revenues $ 1,073,298 1,080,534
Maximum number of months following end of annual period in which revenues are earned to be included in incentive programs 24 months  
Operating Segments    
Disaggregation of Revenue [Line Items]    
Total operating revenues [1],[2] $ 1,073,298 1,080,534
Retail    
Disaggregation of Revenue [Line Items]    
Total revenue from contracts with customers 906,740 930,845
Retail | Residential    
Disaggregation of Revenue [Line Items]    
Total revenue from contracts with customers 458,091 462,908
Retail | Commercial and industrial (C&I)    
Disaggregation of Revenue [Line Items]    
Total revenue from contracts with customers 436,413 455,199
Retail | Other    
Disaggregation of Revenue [Line Items]    
Total revenue from contracts with customers 12,236 12,738
Wholesale    
Disaggregation of Revenue [Line Items]    
Total revenue from contracts with customers 47,890 43,576
Transmission    
Disaggregation of Revenue [Line Items]    
Total revenue from contracts with customers 12,252 14,639
Other    
Disaggregation of Revenue [Line Items]    
Total revenue from contracts with customers 43,760 39,305
Regulated Electric    
Disaggregation of Revenue [Line Items]    
Total revenue from contracts with customers 662,024 681,716
Alternative revenue and other 36,250 29,672
Total operating revenues 698,386 711,480
Regulated Electric | Operating Segments    
Disaggregation of Revenue [Line Items]    
Total operating revenues [1] 698,274 711,388
Regulated Electric | Retail    
Disaggregation of Revenue [Line Items]    
Total revenue from contracts with customers 583,051 606,806
Regulated Electric | Retail | Residential    
Disaggregation of Revenue [Line Items]    
Total revenue from contracts with customers 227,649 234,434
Regulated Electric | Retail | Commercial and industrial (C&I)    
Disaggregation of Revenue [Line Items]    
Total revenue from contracts with customers 343,226 359,697
Regulated Electric | Retail | Other    
Disaggregation of Revenue [Line Items]    
Total revenue from contracts with customers 12,176 12,675
Regulated Electric | Wholesale    
Disaggregation of Revenue [Line Items]    
Total revenue from contracts with customers 47,890 43,576
Regulated Electric | Transmission    
Disaggregation of Revenue [Line Items]    
Total revenue from contracts with customers 12,252 14,639
Regulated Electric | Other    
Disaggregation of Revenue [Line Items]    
Total revenue from contracts with customers 18,831 16,695
Regulated Natural Gas    
Disaggregation of Revenue [Line Items]    
Total revenue from contracts with customers 338,703 334,762
Alternative revenue and other 25,283 21,374
Total operating revenues 364,050 356,192
Regulated Natural Gas | Operating Segments    
Disaggregation of Revenue [Line Items]    
Total operating revenues 363,986 356,136
Regulated Natural Gas | Retail    
Disaggregation of Revenue [Line Items]    
Total revenue from contracts with customers 313,774 312,152
Regulated Natural Gas | Retail | Residential    
Disaggregation of Revenue [Line Items]    
Total revenue from contracts with customers 227,746 225,910
Regulated Natural Gas | Retail | Commercial and industrial (C&I)    
Disaggregation of Revenue [Line Items]    
Total revenue from contracts with customers 86,028 86,242
Regulated Natural Gas | Retail | Other    
Disaggregation of Revenue [Line Items]    
Total revenue from contracts with customers 0 0
Regulated Natural Gas | Wholesale    
Disaggregation of Revenue [Line Items]    
Total revenue from contracts with customers 0 0
Regulated Natural Gas | Transmission    
Disaggregation of Revenue [Line Items]    
Total revenue from contracts with customers 0 0
Regulated Natural Gas | Other    
Disaggregation of Revenue [Line Items]    
Total revenue from contracts with customers 24,929 22,610
All Other    
Disaggregation of Revenue [Line Items]    
Total revenue from contracts with customers 9,915 11,887
Alternative revenue and other 1,123 1,123
Total operating revenues 11,038 13,010
All Other | Operating Segments    
Disaggregation of Revenue [Line Items]    
Total operating revenues [2] 11,038 13,010
All Other | Retail    
Disaggregation of Revenue [Line Items]    
Total revenue from contracts with customers 9,915 11,887
All Other | Retail | Residential    
Disaggregation of Revenue [Line Items]    
Total revenue from contracts with customers 2,696 2,564
All Other | Retail | Commercial and industrial (C&I)    
Disaggregation of Revenue [Line Items]    
Total revenue from contracts with customers 7,159 9,260
All Other | Retail | Other    
Disaggregation of Revenue [Line Items]    
Total revenue from contracts with customers 60 63
All Other | Wholesale    
Disaggregation of Revenue [Line Items]    
Total revenue from contracts with customers 0 0
All Other | Transmission    
Disaggregation of Revenue [Line Items]    
Total revenue from contracts with customers 0 0
All Other | Other    
Disaggregation of Revenue [Line Items]    
Total revenue from contracts with customers $ 0 $ 0
[1] Operating revenues include $1 million and $2 million of affiliate electric revenue for the three months ended March 31, 2018 and 2017.
[2] Operating revenues include $1 million of other affiliate revenue for the three months ended March 31, 2018 and 2017.