Related Party Transactions - Schedule of Related Party Balances (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Related Party Transaction [Line Items]
Owed By		$ 1
Iberdrola, S.A.
Related Party Transaction [Line Items]
Owed By	$ 1
Owed To	(32)	(42)
Iberdrola Renovables Energía, S.L.
Related Party Transaction [Line Items]
Owed To	(6)	0
Iberdrola Financiación, S.A.
Related Party Transaction [Line Items]
Owed To	(4)	0
Vineyard Wind
Related Party Transaction [Line Items]
Owed By	3	5
Iberdrola Solutions
Related Party Transaction [Line Items]
Owed By	2	0
Owed To	(4)
Siemens-Gamesa
Related Party Transaction [Line Items]
Owed To		(18)
Other
Related Party Transaction [Line Items]
Owed By	1	4
Owed To	$ (1)	$ (4)