Quarterly Consolidated Financial Data (unaudited) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Quarterly Financial Information Disclosure [Abstract]
Total Operating revenues	$ 1,367	$ 1,996	$ 879	$ 1,236	$ 1,459	$ 2,209	$ 1,633	$ 1,499	$ 5,478	$ 6,800	$ 6,545
Income (loss) from operations	295	705	(193)	195	196	403	183	18	1,002	800	901
Net income (loss) attributable to Calpine	$ 100	$ 437	$ (329)	$ (9)	$ (13)	$ 190	$ (70)	$ (297)	$ 199	$ (190)	$ 31
Net income (loss) per common share attributable to Calpine — basic (in dollars per share)	$ 0.22	$ 0.95	$ (0.69)	$ (0.02)	$ (0.03)	$ 0.39	$ (0.14)	$ (0.61)	$ 0.43	$ (0.39)	$ 0.06
Net income (loss) per common share attributable to Calpine — diluted (in dollars per share)	$ 0.22	$ 0.94	$ (0.69)	$ (0.02)	$ (0.03)	$ 0.39	$ (0.14)	$ (0.61)	$ 0.42	$ (0.39)	$ 0.06