Capital Structure (Details) (USD $)	12 Months Ended			3 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Mar. 31, 2015	Dec. 31, 2011
Class of Stock [Line Items]
Shares issued under Calpine Equity Incentive Plans	2,566,799	3,022,128	1,741,909
Share repurchase program	(49,684,523)	(31,032,110)	26,436,677
Total common shares outstanding, ending balance	(381,921,264)	(429,038,988)	(457,048,970)		(481,743,738)
Common Stock, authorized shares (in shares)	(1,400,000,000)	(1,400,000,000)
Common Stock, issued shares (in shares)	(502,287,022)	(497,841,056)
Common Stock, par value (in dollars per share)	$ (0.001)	$ (0.001)
Common Stock, outstanding shares (in shares)	(381,921,264)	(429,038,988)
Treasury Stock, Shares (in shares)	120,365,758	68,802,068
Treasury Stock, Value	$ 2,345,000,000	$ 1,230,000,000
Treasury Stock, Value, Acquired, Cost Method	(1,115,000,000)	(636,000,000)	(469,000,000)
Shareholder Transaction
Shareholder Ownership Percentage	10.00%
Common Stock Purchased from Shareholder	13,213,372
Purchase Price of Common Stock Purchased from Shareholder	311,464,283
Shares Issued [Member]
Class of Stock [Line Items]
Shares issued under Calpine Equity Incentive Plans	4,445,966	5,345,956	2,026,285
Share repurchase program	0	0	0
Total common shares outstanding, ending balance	(502,287,022)	(497,841,056)	(492,495,100)		(490,468,815)
Treasury Stock [Member]
Class of Stock [Line Items]
Shares issued under Calpine Equity Incentive Plans	1,879,167	2,323,828	284,376
Share repurchase program	(49,684,523)	(31,032,110)	26,436,677
Total common shares outstanding, ending balance	(120,365,758)	(68,802,068)	(35,446,130)		(8,725,077)
Share Repurchases in 2014 [Member]
Class of Stock [Line Items]
Share repurchase program	(36,471,151)
Treasury Stock, Value, Acquired, Cost Method	(789,000,000)
Treasury Stock Acquired, Average Cost Per Share	$ 21.62
Subsequent Event [Member] | 2014 Through Filing Date [Member]
Class of Stock [Line Items]
Share repurchase program				(5,772,440)
Treasury Stock, Value, Acquired, Cost Method				$ (125,000,000)
Treasury Stock Acquired, Average Cost Per Share				$ 21.68