Assets and Liabilities with Recurring Fair Value Measurements (Textuals) (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Fair Value Measurement [Domain]
Fair Value Disclosures [Abstract]
Cash and Cash Equivalents, at Carrying Value		$ 16		$ 16		$ 23
Restricted Cash and Cash Equivalents		149		149		145
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis with Unobservable Inputs		105	$ 129	(8)	$ 197
Included in operating revenues	[1]	152	31	197	(28)
Fair Value, Assets Measured with Unobservable Inputs on Recurring Basis, Gain (Loss) Included In Fuel And Purchased Energy Expense	[2]	1	18	2	15
Amount of Change in Collateral of Financial Instruments Classified as Derivative Asset (Liability)		(1)	1	1	(1)
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Purchases		1	5	3	9
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Issues		(1)	0	(1)	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		(35)	(42)	28	(53)
Fair Value, Liabilities, Level 1 to Level 2 Transfers, Amount		0	0	0	0
Fair Value, Liabilities, Level 2 to Level 1 Transfers, Amount		0	0	0	0
Transfers into level 3	[3],[4]	6	(1)	7	(1)
Transfers out of Level 3	[4],[5]	(1)	(10)	(2)	(7)
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis with Unobservable Inputs		227	131	227	131
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		153	$ 49	199	$ (13)
Cash and Cash Equivalents, at Carrying Value		297		297		205
Restricted Cash and Cash Equivalents		262		262		201
Fair Value, Inputs, Level 1 [Member]
Fair Value Disclosures [Abstract]
Derivative, Collateral, Right to Reclaim Cash, Net		90		90		(1)
Fair Value, Inputs, Level 2 [Member]
Fair Value Disclosures [Abstract]
Derivative, Collateral, Right to Reclaim Cash, Net		55		55		48
Fair Value, Inputs, Level 3 [Member]
Fair Value Disclosures [Abstract]
Derivative, Collateral, Right to Reclaim Cash, Net		$ 1		$ 1		$ 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] We had $6 million in gains and $(1) million in losses transferred out of level 2 into level 3 for the three months ended June 30, 2019 and 2018, respectively, and $7 million in gains and $(1) million in losses transferred out of level 2 into level 3 for the six months ended June 30, 2019 and 2018, respectively, due to changes in market liquidity in various power markets.

[4] We transfer amounts among levels of the fair value hierarchy as of the end of each period. There were no transfers into or out of level 1 for each of the three and six months ended June 30, 2019 and 2018.

[5] We had $1 million and $10 million in gains transferred out of level 3 into level 2 for the three months ended June 30, 2019 and 2018, respectively, and $2 million and $7 million in gains transferred out of level 3 into level 2 for the six months ended June 30, 2019 and 2018, respectively, due to changes in market liquidity in various power markets.