Assets and Liabilities with Recurring Fair Value Measurements (Textuals) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair Value Measurement [Domain]
Fair Value Disclosures [Abstract]
Cash and Cash Equivalents, at Carrying Value		$ 23	$ 21
Cash Equivalents Included In Restricted Cash, Fair Value Disclosure		145	110
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis with Unobservable Inputs		197	416	$ (46)
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Change in Unrealized Gain (Loss)		(133)	82	(39)
Fair Value, Liabilities, Level 2 to Level 1 Transfers, Amount		0	0	0
Included in operating revenues	[1]	(88)	32	(46)
Included in fuel and purchased energy expense	[2]	(45)	50	7
Amount of Change in Collateral of Financial Instruments Classified as Derivative Asset (Liability)		0	(17)	17
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Purchases	[3]	18	4	426
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Issues		(2)	(1)	0
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Settlements		(86)	(179)	(21)
Fair Value, Liabilities, Level 1 to Level 2 Transfers, Amount		0	0	0
Transfers into level 3	[4],[5]	0	2	(4)
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Transfers out of Level 3	[5],[6]	2	106	(75)
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis with Unobservable Inputs		(8)	197	416
Cash and Cash Equivalents, at Carrying Value		205	284
Cash Equivalents Included In Restricted Cash, Fair Value Disclosure		201	159
Fair Value, Inputs, Level 1 [Member]
Fair Value Disclosures [Abstract]
Derivative, Collateral, Right to Reclaim Cash, Net		(1)	44
Transfer to Level 2 [Member]
Purchases, issuances and settlements:
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Transfers out of Level 3		2	104	(75)
Fair Value Disclosures [Abstract]
Derivative, Collateral, Right to Reclaim Cash, Net		48	18
Fair Value, Inputs, Level 3 [Member]
Fair Value Disclosures [Abstract]
Derivative, Collateral, Right to Reclaim Cash, Net		$ 0	0
Other Assets [Member]
Purchases, issuances and settlements:
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Transfers out of Level 3			$ 2
Calpine Solutions [Member]
Purchases, issuances and settlements:
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Purchases				$ 421

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

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

[3] During December 2016, we had $421 million in purchases related to the acquisition of Calpine Solutions, formerly Noble Solutions.

[4] We had nil and $(2) million in losses and $4 million in gains transferred out of level 2 into level 3 for the years ended December 31, 2018, 2017 and 2016, respectively.

[5] 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 during the years ended December 31, 2018, 2017 and 2016.

[6] We had $2 million and $104 million in gains and $(75) million in losses transferred out of level 3 into level 2 during the years ended December 31, 2018, 2017 and 2016, respectively, due to changes in market liquidity in various power markets and $2 million in gains transferred out of level 3 during the years ended December 31, 2017, to other assets following the election of the normal purchase normal sales exemption and the discontinuance of derivative accounting treatment as of the date of this election for certain commodity contracts.