Condensed Consolidated Statements of Income (unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Operating Revenues	$ 1,546	$ 1,341	$ 4,813	$ 4,430
Operating Expenses
Purchased power, natural gas and fuel used	342	250	1,197	957
Loss from assets held for sale	1	0	16	0
Operations and maintenance	574	531	1,634	1,546
Depreciation and amortization	226	205	644	608
Taxes other than income taxes, net	150	137	444	422
Total Operating Expenses	1,293	1,123	3,935	3,533
Operating Income	253	218	878	897
Other Income and (Expense)
Other expense	(16)	(15)	(57)	(52)
Earnings from equity method investments	1	0	8	3
Interest expense, net of capitalization	(75)	(71)	(219)	(210)
Income Before Income Tax	163	132	610	638
Income tax expense	29	32	128	179
Net Income	134	100	482	459
Less: Net income attributable to noncontrolling interests	9	1	6	1
Net Income Attributable to Avangrid, Inc.	$ 125	$ 99	$ 476	$ 458
Earnings Per Common Share, Basic (in usd per share)	$ 0.40	$ 0.32	$ 1.54	$ 1.48
Earnings Per Common Share, Diluted (in usd per share)	$ 0.40	$ 0.32	$ 1.54	$ 1.48
Weighted-average Number of Common Shares Outstanding:
Basic (in shares)	309,491,082	309,491,082	309,507,443	309,506,831
Diluted (in shares)	309,689,890	309,801,903	309,705,788	309,785,639