Variable Interest Entities and Unconsolidated Investments (VIE Textuals) (Details)		12 Months Ended
		Dec. 31, 2018 USD ($) yr MW	Dec. 31, 2017 USD ($) MW	Dec. 31, 2016 USD ($)
Schedule of Equity Method Investments [Line Items]
Proceeds from sale of power plants and other(2)	[1]	$ 11,000,000	$ 162,000,000	$ 179,000,000
Variable Interest Entity, Financial or Other Support, Amount		0	0	$ 115,000,000
Equity Method Investment, Summarized Financial Information, Debt		301,000,000	256,000,000
Prorata Share of Equity Method Investment, Summarized Financial Information, Debt		151,000,000	128,000,000
Long-term Debt		10,156,000,000	$ 11,213,000,000
Put Option [Member]
Schedule of Equity Method Investments [Line Items]
Proceeds from sale of power plants and other(2)		280,000,000
Call Option [Member]
Schedule of Equity Method Investments [Line Items]
Proceeds from sale of power plants and other(2)		$ 377,000,000
Russell City Energy [Member]
Schedule of Equity Method Investments [Line Items]
Minority Interest Ownership Percentage By Noncontrolling Third Party Owners		25.00%
Equity Method Investment, Ownership Percentage		75.00%
Variable Interest Entity, Primary Beneficiary [Member]
Schedule of Equity Method Investments [Line Items]
Power generation capacity | MW		7,880	7,880
Inland Empire Energy Center [Member]
Schedule of Equity Method Investments [Line Items]
Power generation capacity | MW		775
Put Option Exercise Period | yr		2,025
Minimum [Member] | Inland Empire Energy Center [Member]
Schedule of Equity Method Investments [Line Items]
Call Option Exercise Period | yr		2,017
Maximum [Member] | Inland Empire Energy Center [Member]
Schedule of Equity Method Investments [Line Items]
Call Option Exercise Period | yr		2,024
Calpine Receivables [Member]
Schedule of Equity Method Investments [Line Items]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount		$ 44,000,000
Equity Method Investment, Ownership Percentage		100.00%
Greenfield [Member]
Schedule of Equity Method Investments [Line Items]
Power generation capacity | MW		1,038
Equity Method Investment, Ownership Percentage		50.00%
Whitby [Member]
Schedule of Equity Method Investments [Line Items]
Power generation capacity | MW		50
Equity Method Investment, Ownership Percentage		50.00%
OMEC [Member]
Schedule of Equity Method Investments [Line Items]
Debt Instrument, Face Amount		$ 220,000,000
Long-term Debt	[2]	$ 218,000,000	$ 294,000,000

[1] On October 26, 2016, we completed the sale of Mankato Power Plant for $407 million, including working capital and other adjustments. We received net proceeds of $164 million after the non-cash reduction of Steamboat project debt of $243 million as the funds were provided directly to the lender in conjunction with the sale of the power plant.

[2] On December 19, 2018, we refinanced the project debt associated with OMEC which lowered the aggregate debt balance to $220 million and extended the maturity to August 2024. In the event that the OMEC put option is exercised, the debt will become payable on November 3, 2019. See Note 7 for further information related to the OMEC put option.