Stock-Based Compensation (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011		Jun. 30, 2010
Summary of non-qualified stock option activity for Calpine Equity Incentive Plans [Abstract]
Options Outstanding, Beginning balance, Number			17,164,890
Options Outstanding, Beginning balance, Weighted Average Exercise Price			$ 17.44
Options Ouststanding, Beginning balance, Weighted Average Remaining Term (in years)			5.6
Options Outstanding, Beginning balance, Aggregate Intrinsic Value (in $ millions)			$ 8,000,000
Options granted during the period, number			909,306
Options granted during the period, Weighted Average Exercise Price	$ 14.32		$ 14.32
Options exercised during the period, Number			6,654
Options exercised during the period, Weighted Average Exercise Price	$ 10.95		$ 10.95
Options forfeited during the period, Number			51,050
Options forfeited during the period, Weighted Average Exercise Price	$ 11.23		$ 11.23
Options expired during the period, Number			156,885
Options expired during the period, Weighted Average Exercise Price	$ 17.55		$ 17.55
Options Outstanding, Ending balance, Number	17,859,607		17,859,607
Options Outstanding, Ending balance, Weighted Average Exercise Price	$ 17.30		$ 17.30
Options Ouststanding, Ending balance, Weighted Average Remaining Term (in years)	5.3		5.3
Options Outstanding, Ending balance, Aggregate Intrinsic Value (in $ millions)	25,000,000		25,000,000
Options Exercisable, Ending balance, Number	6,665,499		6,665,499
Options Exercisable, Ending balance, Weighted Average Exercise Price	$ 19.15		$ 19.15
Options Exercisable, Ending balance, Weighted Average Remaining Term (in years)			5.3
Options Exercisable, Ending balance, Aggregate Intrinsic Value (in $ millions)	1,000,000		1,000,000
Options Vested and Expected to Vest, Ending balance, Number	17,443,021		17,443,021
Options Vested and Expected to Vest, Ending balance, Weighted Average Exercise Price	$ 17.41		$ 17.41
Options Vested and Expected to Vest, Ending balance, Weighted Average Remaining Term (in years)			5.2
Options Vested and Expected to Vest, Ending balance, Aggregate Intrinsic Value (in $ millions)	24,000,000		24,000,000
Share-based Compensation Arrangement Fair Value Assumptions and Methodology [Abstract]
Expected term (in years)			6.5	[1]	6.5	[1]
Dividend yield				[2]		[2]
Weighted average grant-date fair value (per option)			$ 5.48		$ 4.66
Restricted Stock and Stock Unit Activity [Abstract]
Nonvested Restricted Stock, Beginning balance, Number			2,683,117
Nonvested Restricted Stock, Beginning balance, Weighted Average Grant Date Fair Value			$ 11.16
Nonvested Restricted Stock granted during the period, number			1,630,465
Nonvested Restricted Stock, granted during the period, Weighted Average Grant Date Fair Value			$ 14.38
Nonvested Restricted Stock forfeited during the period, Number			145,923
Nonvested Restricted Stock forfeited during the period, Weighted Average Grant Date Fair Value	$ 11.88		$ 11.88
Nonvested Restricted Stock vested during the period during the period, Number			460,232
Nonvested Restricted Stock vested during the period, Weighted Average Grant Date Fair Value			$ 14.62
Nonvested Restricted Stock, Ending balance, Number	3,707,427		3,707,427
Nonvested Restricted Stock, Ending balance, Weighted Average Grant Date Fair Value	$ 12.10		$ 12.10
Stock-Based Compensation (Textuals) [Abstract]
Vesting period for graded and cliff vesting options - minimum			1
Vesting period for graded and cliff vesting options - maximum			5
Contractual terms for the graded and cliff vesting options - minimum			5
Contractual terms for the graded and cliff vesting options - maximum			10
Common stock authorized for issuance under the Director Plan	567,000		567,000
Common stock authorized for issuance under the Equity Plan	27,533,000		27,533,000
Percentage of sub-grants representing the total	33.33%		33.33%
First sub-grant vesting term	1		1
Second sub-grant vesting term	2		2
Third sub-grant vesting term	3		3
Number of grants in option grants with three year cliff vesting	1		1
Vesting term of option grants with three year cliff vesting	3		3
Stock-based compensation expense	7,000,000	6,000,000	12,000,000		12,000,000
Total FV of vested restricted stock and restricted stock units			7,000,000		4,000,000
Minimum
Share-based Compensation Arrangement Fair Value Assumptions and Methodology [Abstract]
Risk-free interest rate			2.70%	[3]	2.90%	[3]
Expected volatility			31.20%	[4]	35.00%	[4]
Maximum
Share-based Compensation Arrangement Fair Value Assumptions and Methodology [Abstract]
Risk-free interest rate			3.20%	[3]	3.30%	[3]
Expected volatility			31.70%	[4]	37.60%	[4]
Stock options
Share-based Compensation Arrangement Fair Value Assumptions and Methodology [Abstract]
Total unrecognized compensation cost related to share based awards	17,000,000		17,000,000
Weighted average period for share based awards to be recognized			1.6
Restricted stock
Share-based Compensation Arrangement Fair Value Assumptions and Methodology [Abstract]
Total unrecognized compensation cost related to share based awards	22,000,000		22,000,000
Weighted average period for share based awards to be recognized			1.8
Restricted stock units
Share-based Compensation Arrangement Fair Value Assumptions and Methodology [Abstract]
Total unrecognized compensation cost related to share based awards	$ 1,000,000		$ 1,000,000
Weighted average period for share based awards to be recognized			0.9

[1] Expected term calculated using the simplified method prescribed by the SEC due to the lack of sufficient historical exercise data to provide a reasonable basis to estimate the expected term.

[2] We have never paid cash dividends on our common stock, and it is not anticipated that any cash dividends will be paid on our common stock in the near future.

[3] Zero Coupon U.S. Treasury rate or equivalent based on expected term.

[4] Volatility calculated using the implied volatility of our exchange traded stock options.