Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net Income		$ 239	$ 212
Other Comprehensive Income, Net of Tax Amounts arising during the period:
Gain on defined benefit plans, net of income tax			4
Unrealized gain during the period on derivatives qualifying as cash flow hedges, net of income taxes		2	2
Reclassification to net income of losses (gains) on cash flow hedges, net of income taxes	[1]	23	(26)
Other Comprehensive Income (Loss)		25	(20)
Comprehensive Income		264	192
Comprehensive Income Attributable to Avangrid, Inc.		$ 264	$ 192

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