Equity Method Investments (Details) $ in Millions	1 Months Ended	3 Months Ended	9 Months Ended
	Oct. 31, 2020 MW	Mar. 31, 2020 MW	Sep. 30, 2020 USD ($) mi² MW	Dec. 31, 2019 USD ($)
Schedule of Equity Method Investments [Line Items]
Production capacity (in MW) | MW			3,000
Equity method investments			$ 668	$ 645
AC Transmission Public Policy Project, total cost			600
Amount receivable from equity method investment investee				1
Vineyard Wind, LLC
Schedule of Equity Method Investments [Line Items]
Proposed offshore wind farm capacity (in MW) | MW		804
Equity method investments			261	227
Vineyard Wind, LLC | Subsequent Event | Min.
Schedule of Equity Method Investments [Line Items]
Proposed offshore wind farm capacity (in MW) | MW	1,200
Vineyard Wind, LLC | Subsequent Event | Max.
Schedule of Equity Method Investments [Line Items]
Proposed offshore wind farm capacity (in MW) | MW	1,300
New York TransCo.
Schedule of Equity Method Investments [Line Items]
Amount receivable from equity method investment investee			$ 0	$ 0
Renewables | Vineyard Wind, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage			50.00%
Contributions to equity method investment			$ 157
Renewables | Second Offshore Development Project
Schedule of Equity Method Investments [Line Items]
Contributions to equity method investment			$ 110
Networks | New York TransCo.
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage			20.00%
Contributions to equity method investment			$ 120
Vineyard Wind, LLC
Schedule of Equity Method Investments [Line Items]
Area of land (in square-mile) | mi²			260
CIP
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage				50.00%