Capital Structure (Details) - USD ($) $ / shares in Units, $ in Billions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Mar. 08, 2018	Dec. 31, 2016
Class of Stock [Line Items]
Sale of Stock, Price Per Share					$ 15.25
Sale of Stock, Consideration Received on Transaction	$ 5.6
Common Stock, authorized shares (in shares)		5,000	5,000
Common Stock, issued shares (in shares)		105.2	105.2
Treasury Stock, Shares
Common Stock, par value (in dollars per share)		$ 0.001	$ 0.001
Common Stock, outstanding shares (in shares)		105.2	105.2	360,516,091		359,061,764
Shares issued under Calpine Equity Incentive Plans		0	(121,906)	1,454,327
Stock Canceled During the Period, Shares			(360,394,185)
Stock Issued During Period, Shares, New Issues			105.2
Shares Issued [Member]
Class of Stock [Line Items]
Common Stock, issued shares (in shares)		105.2	105.2	361,677,891		359,627,113
Shares issued under Calpine Equity Incentive Plans		0	355,805	2,050,778
Stock Canceled During the Period, Shares			(362,033,696)
Stock Issued During Period, Shares, New Issues			105.2
Treasury Stock [Member]
Class of Stock [Line Items]
Treasury Stock, Shares		0	0	1,161,800		565,349
Shares issued under Calpine Equity Incentive Plans		0	(477,711)	(596,451)
Stock Canceled During the Period, Shares			1,639,511
Stock Issued During Period, Shares, New Issues			0