Assets and Liabilities with Recurring Fair Value Measurements (Textuals) (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Mar. 31, 2019
Fair Value Measurement [Domain]
Fair Value Disclosures [Abstract]
Cash and Cash Equivalents, at Carrying Value		$ 190		$ 190		$ 573
Restricted Cash and Cash Equivalents		227		227		211
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis with Unobservable Inputs		249	$ 105	171	$ (8)
Included in operating revenues	[1]	37	152	106	197
Fair Value, Assets Measured with Unobservable Inputs on Recurring Basis, Gain (Loss) Included In Fuel And Purchased Energy Expense	[2]	3	1	(1)	2
Amount of Change in Collateral of Financial Instruments Classified as Derivative Asset (Liability)		0	(1)	0	1
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Purchases		1	1	1	3
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Issues		0	(1)	0	(1)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		(49)	(35)	(36)	28
Fair Value, Liabilities, Level 1 to Level 2 Transfers, Amount							$ 0
Fair Value, Liabilities, Level 2 to Level 1 Transfers, Amount		0		0			$ 0
Transfers into level 3	[3],[4]	10	6	11	7
Transfers out of Level 3	[3],[5]	(5)	(1)	(6)	(2)
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis with Unobservable Inputs		246	227	246	227
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		40	$ 153	105	$ 199
Cash and Cash Equivalents, at Carrying Value		677		677		1,131
Restricted Cash and Cash Equivalents		241		241		345
Level 1
Fair Value Disclosures [Abstract]
Derivative, Collateral, Right to Reclaim Cash, Net		10		10		112
Level 2
Fair Value Disclosures [Abstract]
Derivative, Collateral, Right to Reclaim Cash, Net		(3)		(3)		2
Level 3
Fair Value Disclosures [Abstract]
Derivative, Collateral, Right to Reclaim Cash, Net		$ 0		$ 0		$ 0

[1] For power contracts and other power-related products, included on our Consolidated Condensed Statements of Operations.

[2] For natural gas and power contracts, swaps and options, included on our Consolidated Condensed Statements of Operations.

[3] (2)Amount represents the arithmetic average of the significant unobservable input based on the range disclosed.

[4] We had $10 million and $6 million in gains transferred out of level 2 into level 3 for the three months ended June 30, 2020 and 2019, respectively, and $11 million and $7 million in gains transferred out of level 2 into level 3 for the six months ended June 30, 2020 and 2019, respectively, due to changes in market liquidity in various power markets.

[5] We had $5 million and $1 million in gains transferred out of level 3 into level 2 for the three months ended June 30, 2020 and 2019, respectively, and $6 million and $2 million in gains transferred out of level 3 into level 2 for the six months ended June 30, 2020 and 2019, respectively, due to changes in market liquidity in various power markets.