Cover Page - shares	9 Months Ended
Cover Page - shares	Sep. 30, 2020	Oct. 29, 2020
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2020
Document Transition Report	false
Entity File Number	001-37660
Entity Registrant Name	Avangrid, Inc.
Entity Incorporation, State or Country Code	NY
Entity Tax Identification Number	14-1798693
Entity Address, Address Line One	180 Marsh Hill Road
Entity Address, City or Town	Orange,
Entity Address, State or Province	CT
Entity Address, Postal Zip Code	06477
City Area Code	207
Local Phone Number	629-1200
Title of 12(b) Security	Common Stock, par value $0.01 per share
Trading Symbol	AGR
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		309,009,817
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Entity Central Index Key	0001634997
Current Fiscal Year End Date	--12-31

Condensed Consolidated Statements of Income (unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Operating Revenues	$ 1,470	$ 1,487	$ 4,651	$ 4,729
Operating Expenses
Purchased power, natural gas and fuel used	259	279	999	1,101
Operations and maintenance	634	588	1,788	1,714
Depreciation and amortization	255	237	748	681
Taxes other than income taxes	157	144	469	446
Total Operating Expenses	1,305	1,248	4,004	3,942
Operating Income	165	239	647	787
Other Income and (Expense)
Other income	16	6	15	1
Earnings (losses) from equity method investments	1	(1)	(3)	1
Interest expense, net of capitalization	(86)	(72)	(251)	(226)
Income Before Income Tax	96	172	408	563
Income tax expense	15	33	21	103
Net Income	81	139	387	460
Net loss attributable to noncontrolling interests	6	11	28	17
Net Income Attributable to Avangrid, Inc.	$ 87	$ 150	$ 415	$ 477
Earnings Per Common Share, Basic (in usd per share)	$ 0.28	$ 0.48	$ 1.34	$ 1.54
Earnings Per Common Share, Diluted (in usd per share)	$ 0.28	$ 0.48	$ 1.34	$ 1.54
Weighted-average Number of Common Shares Outstanding:
Basic (in shares)	309,491,082	309,491,082	309,496,234	309,491,082
Diluted (in shares)	309,550,126	309,517,778	309,554,838	309,512,301

Condensed Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement of Comprehensive Income [Abstract]
Net Income	$ 81	$ 139	$ 387	$ 460
Other Comprehensive Income (Loss)
Loss on nonqualified pension plans	0	0	0	(1)
Unrealized (loss) gain during the period on derivatives qualifying as cash flow hedges, net of income tax of $(3) and $2 for the three months ended, respectively, and $(8) for both the nine months ended	(15)	5	(31)	(22)
Reclassification to net income of loss on cash flow hedges, net of income taxes of $0 and $1 for both the three months ended, respectively, and $1 and $2 for the nine months ended, respectively	9	5	12	8
Other Comprehensive Income (Loss)	(6)	10	(19)	(15)
Comprehensive Income	75	149	368	445
Net loss attributable to noncontrolling interests	6	11	28	17
Comprehensive Income Attributable to Avangrid, Inc.	81	160	396	462
Unrealized gain (loss) during the period on derivatives qualifying as cash flow hedges, tax	$ (3)	$ 2	$ (8)	$ (8)

Condensed Consolidated Statements of Comprehensive Income (unaudited) (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement of Comprehensive Income [Abstract]
Unrealized (loss) gain during the period on derivatives qualifying as cash flow hedges, tax	$ (3)	$ 2	$ (8)	$ (8)
Reclassification to net income of loss on cash flow hedges, tax expense (benefit)	$ 0	$ 1	$ 1	$ 2

Condensed Consolidated Balance Sheets (unaudited) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Current Assets
Cash and cash equivalents	$ 101	$ 178
Accounts receivable and unbilled revenues, net	1,021	1,082
Accounts receivable from affiliates	7	10
Derivative assets	19	11
Fuel and gas in storage	100	110
Materials and supplies	157	141
Prepayments and other current assets	266	199
Regulatory assets	252	294
Total Current Assets	1,923	2,025
Total Property, Plant and Equipment ($1,657 and $787 related to VIEs, respectively)	26,432	25,218
Operating lease right-of-use assets	68	70
Equity method investments	668	645
Other investments	61	63
Regulatory assets	2,591	2,567
Other Assets
Goodwill	3,119	3,119
Intangible assets	307	314
Derivative assets	85	84
Other	386	311
Total Other Assets	3,897	3,828
Total Assets	35,640	34,416
Current Liabilities
Current portion of debt	813	730
Notes payable	998	560
Notes payable to affiliates	4	0
Interest accrued	87	72
Accounts payable and accrued liabilities	1,481	1,361
Accounts payable to affiliates	43	64
Dividends payable	136	136
Taxes accrued	82	56
Operating lease liabilities	11	12
Derivative liabilities	19	20
Other current liabilities	296	334
Regulatory liabilities	214	242
Total Current Liabilities	4,184	3,587
Regulatory liabilities	3,342	3,281
Other Non-current Liabilities
Deferred income taxes	1,846	1,814
Deferred income	1,221	1,274
Pension and other postretirement	998	1,100
Operating lease liabilities	42	65
Derivative liabilities	81	85
Asset retirement obligations	208	190
Environmental remediation costs	333	338
Other	450	380
Total Other Non-current Liabilities	5,179	5,246
Non-current debt	7,081	6,716
Total Non-current Liabilities	15,602	15,243
Total Liabilities	19,786	18,830
Commitments and Contingencies
Stockholders’ Equity:
Common stock, $.01 par value, 500,000,000 shares authorized, 309,794,917 and 309,752,140 shares issued; 309,005,485 and 309,005,272 shares outstanding, respectively	3	3
Additional paid in capital	13,664	13,660
Treasury stock	(14)	(12)
Retained earnings	1,684	1,681
Accumulated other comprehensive loss	(114)	(95)
Total Stockholders’ Equity	15,223	15,237
Non-controlling interests	631	349
Total Equity	15,854	15,586
Total Liabilities and Equity	$ 35,640	$ 34,416

Condensed Consolidated Balance Sheets (unaudited) (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Property, plant and equipment	$ 26,432	$ 25,218
Common stock, par value (in USD per share)	$ 0.01	$ 0.01
Common stock, authorized (in shares)	500,000,000	500,000,000
Common stock, issued (in shares)	309,794,917	309,752,140
Common stock, outstanding (in shares)	309,005,485	309,005,272
Variable Interest Entity, Primary Beneficiary
Property, plant and equipment	$ 1,657		$ 787

Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash Flow from Operating Activities:
Net Income	$ 387	$ 460
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	748	681
Regulatory assets/liabilities amortization and carrying cost	63	51
Pension cost	60	68
Earnings (losses) from equity method investments	3	(1)
Distributions of earnings received from equity method investments	15	10
Unrealized gain on marked-to-market derivative contracts	(9)	(66)
Deferred taxes	11	99
Other non-cash items	(35)	(35)
Changes in operating assets and liabilities:
Current assets	7	188
Noncurrent assets	(152)	(24)
Current liabilities	24	(73)
Noncurrent liabilities	(30)	(114)
Net Cash Provided by Operating Activities	1,092	1,244
Cash Flow from Investing Activities:
Capital expenditures	(1,960)	(2,045)
Contributions in aid of construction	35	36
Proceeds from sale of assets	12	13
Proceeds from notes receivable from affiliates	2	0
Distributions received from equity method investments	3	4
Other investments and equity method investments, net	(48)	(164)
Net Cash Used in Investing Activities	(1,956)	(2,156)
Cash Flow from Financing Activities:
Non-current debt issuances	967	1,637
Repayments of non-current debt	(511)	(344)
Receipts of other short-term debt, net	441	32
Repayments of financing leases	(7)	(26)
Repurchase of common stock	(2)	0
Issuance of common stock	(1)	0
Distributions to noncontrolling interests	(5)	(47)
Contributions from noncontrolling interests	312	133
Dividends paid	(408)	(408)
Net Cash Provided by Financing Activities	786	977
Net (Decrease) Increase in Cash, Cash Equivalents and Restricted Cash	(78)	65
Cash, Cash Equivalents and Restricted Cash, Beginning of Period	184	43
Cash, Cash Equivalents and Restricted Cash, End of Period	106	108
Supplemental Cash Flow Information
Cash paid for interest, net of amounts capitalized	206	183
Cash paid for income taxes	$ 4	$ 4

Condensed Consolidated Statements of Changes in Equity (unaudited) - USD ($)
$ in Millions

Total