Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net Income		$ 120	$ 102	$ 359	$ 314
Other Comprehensive Income, Net of Tax Amounts arising during the period:
Gain on defined benefit plans, net of income taxes					4
Unrealized (loss) gain during the period on derivatives qualifying as cash flow hedges, net of income taxes			(23)	2	(21)
Reclassification to net income of losses (gains) on cash flow hedges, net of income taxes	[1]	(1)	1	22	(25)
Other Comprehensive Income (Loss)		(1)	(22)	24	(42)
Comprehensive Income		119	80	383	272
Comprehensive Income Attributable to Avangrid, Inc.		$ 119	$ 80	$ 383	$ 272

[1] Reclassification is reflected in the operating expenses line item in the condensed consolidated statements of income.