Investments (Unconsolidated Equity Investments) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Schedule of Equity Method Investments [Line Items]
Equity income from unconsolidated investments, net	$ (15)	$ (12)	$ (46)	$ (35)
ATC Holdings [Member]
Schedule of Equity Method Investments [Line Items]
Equity income from unconsolidated investments, net	(11)	(11)	(36)	(30)
Non-utility wind farm in Oklahoma [Member]
Schedule of Equity Method Investments [Line Items]
Equity income from unconsolidated investments, net	(2)	0	(6)	(3)
Other [Member]
Schedule of Equity Method Investments [Line Items]
Equity income from unconsolidated investments, net	$ (2)	$ (1)	$ (4)	$ (2)

Amount of income (loss) for proportionate share of equity method investee's income (loss).

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