Segment Information (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018		Mar. 31, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Total operating revenues(1)	[1]	$ 2,009		$ 2,281
Commodity Margin		612		558
Add: Mark-to-market commodity activity, net and other(2)	[2]	(373)		31
Operating and maintenance expense		275		282
Depreciation and amortization expense		201		206
General and other administrative expense		60		40
Other operating expenses		37		20
Gain on sale of assets, net		0		(27)
(Income) loss from unconsolidated investments in power plants		(6)		(4)
Income (loss) from operations		(328)		72
Interest expense		151		159
Debt Extinguishment Costs and Other (Income) Expense, Net		7		26
Loss before income taxes		(486)		(113)
Lease levelization		(16)		(22)
West [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total operating revenues(1)	[1]	480		519
Commodity Margin		185		203
Add: Mark-to-market commodity activity, net and other(2)	[2]	13		80
Operating and maintenance expense		90		91
Depreciation and amortization expense		67		87
General and other administrative expense		16		12
Other operating expenses		14		9
Gain on sale of assets, net				0
(Income) loss from unconsolidated investments in power plants		0		0
Income (loss) from operations		11		84
Texas [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total operating revenues(1)	[1]	140		608
Commodity Margin		166		125
Add: Mark-to-market commodity activity, net and other(2)	[2]	(547)		43
Operating and maintenance expense		80		81
Depreciation and amortization expense		76		54
General and other administrative expense		25		16
Other operating expenses		16		3
Gain on sale of assets, net				0
(Income) loss from unconsolidated investments in power plants		0		0
Income (loss) from operations		(578)		14
East [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total operating revenues(1)	[1]	614		416
Commodity Margin		184		142
Add: Mark-to-market commodity activity, net and other(2)	[2]	40		14
Operating and maintenance expense		71		81
Depreciation and amortization expense		45		48
General and other administrative expense		15		7
Other operating expenses		7		9
Gain on sale of assets, net				(27)
(Income) loss from unconsolidated investments in power plants		(6)		(4)
Income (loss) from operations		92		42
Retail [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total operating revenues(1)	[1]	938		960
Commodity Margin		77		88
Add: Mark-to-market commodity activity, net and other(2)		128	[2]	(98)
Operating and maintenance expense		40		36
Depreciation and amortization expense		13		17
General and other administrative expense		4		5
Other operating expenses		0		0
Gain on sale of assets, net				0
(Income) loss from unconsolidated investments in power plants		0		0
Income (loss) from operations		148		(68)
Consolidation, Eliminations [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total operating revenues(1)	[1]	(163)		(222)
Commodity Margin		0		0
Add: Mark-to-market commodity activity, net and other(2)	[2]	(7)		(8)
Operating and maintenance expense		(6)		(7)
Depreciation and amortization expense		0		0
General and other administrative expense		0		0
Other operating expenses		0		(1)
Gain on sale of assets, net				0
(Income) loss from unconsolidated investments in power plants		0		0
Income (loss) from operations		(1)		0
Intersegment Eliminations [Member] | West [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total operating revenues(1)		114		61
Intersegment Eliminations [Member] | Texas [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total operating revenues(1)		(67)		72
Intersegment Eliminations [Member] | East [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total operating revenues(1)		115		88
Intersegment Eliminations [Member] | Retail [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total operating revenues(1)		1		1
Other Assets [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Amortization of Intangible Assets		$ 28		$ 60

[1] Includes intersegment revenues of $114 million and $61 million in the West, $(67) million and $72 million in Texas, $115 million and $88 million in the East and $1 million and $1 million in Retail for the three months ended March 31, 2018 and 2017, respectively. Intersegment revenues for sales between wholesale and retail operations are executed to manage supply needs for our retail operations from our wholesale fleet or to facilitate margin collateral netting at Calpine Corporation.

[2] Includes $(16) million and $(22) million of lease levelization and $28 million and $60 million of amortization expense for the three months ended March 31, 2018 and 2017, respectively.