Capital Structure (Details) (USD $)	1 Months Ended	3 Months Ended			12 Months Ended
	Feb. 12, 2013	Mar. 31, 2013	Jun. 30, 2012	Sep. 30, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Class of Stock [Line Items]
Shares Of New, Reorganized Common Stock					485,000,000
Common Stock, authorized shares (in shares)					(1,400,000,000)	(1,400,000,000)
Common Stock, issued shares (in shares)					(492,495,100)	(490,468,815)
Common Stock, par value (in dollars per share)					$ (0.001)	$ (0.001)
Common Stock, outstanding shares (in shares)					(457,048,970)	(481,743,738)
Treasury Stock, Shares (in shares)					35,446,130	8,725,077
Treasury Stock, Value					$ 594,000,000	$ 125,000,000
Stock Repurchase Program, Authorized Amount		400,000,000	600,000,000	300,000,000
Treasury Stock, Value, Acquired, Cost Method					469,000,000	120,000,000	2,000,000
Treasury Stock Acquired, Average Cost Per Share	$ 16.87
Common Stock Activity [Roll Forward]
Total common shares outstanding, beginning balance	(457,048,970)	(457,048,970)			(481,743,738)	(488,693,630)	(487,745,299)
Resolution of claims/inter-creditor disputes						0	0
Shares issued under Calpine Equity Incentive Plans					1,741,909	1,187,181	948,331
Share repurchase program	(35,568,833)				(26,436,677)	(8,137,073)
Total common shares outstanding, ending balance					(457,048,970)	(481,743,738)	(488,693,630)
Stock Repurchase Program, Cumulative Authorized Amount					$ 1,000,000,000
Shares Issued [Member]
Common Stock Activity [Roll Forward]
Total common shares outstanding, beginning balance					(490,468,815)	(444,883,356)	(443,325,827)
Resolution of claims/inter-creditor disputes						44,258,432	488,612
Shares issued under Calpine Equity Incentive Plans					2,026,285	1,327,027	1,068,917
Share repurchase program					0	0
Total common shares outstanding, ending balance					(492,495,100)	(490,468,815)	(444,883,356)
Shares Held inTreasury [Member]
Common Stock Activity [Roll Forward]
Total common shares outstanding, beginning balance					(8,725,077)	(448,158)	(327,572)
Resolution of claims/inter-creditor disputes						0	0
Shares issued under Calpine Equity Incentive Plans					284,376	139,846	120,586
Share repurchase program					(26,436,677)	(8,137,073)
Total common shares outstanding, ending balance					(35,446,130)	(8,725,077)	(448,158)
Shares Held in Reserve [Member]
Common Stock Activity [Roll Forward]
Total common shares outstanding, beginning balance					0	(44,258,432)	(44,747,044)
Resolution of claims/inter-creditor disputes						44,258,432	488,612
Shares issued under Calpine Equity Incentive Plans					0	0	0
Share repurchase program					0	0
Total common shares outstanding, ending balance					0	0	(44,258,432)