CONDENSED FINANCIAL INFORMATION OF PARENT - Statement of Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Condensed Income Statements, Captions [Line Items]
Operating Revenues	$ 6,320	$ 6,336	$ 6,477
Operating Expenses
Taxes other than income taxes, net	619	591	579
Total Operating Expenses	5,451	5,338	5,361
Operating Income	869	998	1,116
Other Income
Other income	18	121	(66)
Interest expense	(316)	(310)	(303)
Income Before Income Tax	568	812	757
Income tax expense	29	169	167
Net Income Attributable to Avangrid, Inc.	581	667	587
AVANGRID
Condensed Income Statements, Captions [Line Items]
Operating Revenues	0	0	0
Operating Expenses
Operating expense	10	3	3
Taxes other than income taxes, net	(11)	(12)	(11)
Total Operating Expenses	(1)	(9)	(8)
Operating Income	1	9	8
Other Income
Other income	35	59	48
Equity earnings of subsidiaries	641	678	596
Interest expense	(109)	(93)	(56)
Income Before Income Tax	568	653	596
Income tax expense	(13)	(14)	9
Net Income Attributable to Avangrid, Inc.	$ 581	$ 667	$ 587