Fair Value of Financial Instruments (Credit Risk - Details 5) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Derivative Fair Value Meaurements and Concentration of Credit Risk
Counterparty credit exposure, excluding credit risk exposure under certain long term agreements		$ 231
Counterparty credit exposure, collateral held (cash and letters of credit) against positions		2
Counterparty credit exposure, net		$ 229
Company's exposure before collateral expected to roll off by the end of 2015 (as a percent)		95.00%
Net exposure (as a percent)	[1],[2]	100.00%
Counterparty credit risk exposure to certain counterparties, threshold (as a percent)		10.00%
Aggregate counterparty credit risk exposure for counterparties representing exposure above threshold percentage		$ 80
Estimated counterparty credit risk exposure under certain long term agreements, including California tolling agreements, South Central load obligations and solar power purchase agreements for the next 5 years		$ 4,100
Period of estimated counterparty credit risk exposure under certain long term agreements, including California tolling agreements, South Central load obligations and solar power purchase agreements (in years)		5 years
Provision for bad debts		$ 48	$ 64	$ 64
Investment grade
Derivative Fair Value Meaurements and Concentration of Credit Risk
Net exposure (as a percent)	[1],[2]	67.00%
External Credit Rating, Non Investment Grade [Member]
Derivative Fair Value Meaurements and Concentration of Credit Risk
Net exposure (as a percent)	[1],[2]	33.00%
Utilities, energy merchants, marketers and other
Derivative Fair Value Meaurements and Concentration of Credit Risk
Net exposure (as a percent)	[1],[2]	100.00%
NRG Yield, Inc. [Member]
Derivative Fair Value Meaurements and Concentration of Credit Risk
Estimated counterparty credit risk exposure under certain long term agreements, including California tolling agreements, South Central load obligations and solar power purchase agreements for the next 5 years		$ 2,600

[1] Counterparty credit exposure excludes uranium and coal transportation contracts because of the unavailability of market prices.

[2] The figures in the tables above exclude potential counterparty credit exposure related to RTOs, ISOs, registered commodity exchanges and certain long term contracts.