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Asset Impairments (Details) - USD ($)			3 Months Ended					12 Months Ended
	Jun. 29, 2018	May 12, 2016	Dec. 31, 2018	Jun. 30, 2018	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Feb. 20, 2019	Mar. 31, 2016
Asset Impairments
Impairment losses								$ 99,000,000	$ 1,534,000,000	$ 483,000,000
Equity method investments			$ 412,000,000					412,000,000	182,000,000
Impairment losses on investments								15,000,000	79,000,000	268,000,000
Emission Allowances
Asset Impairments
Impairment losses									20,000,000	0
Other
Asset Impairments
Impairment losses										29,000,000
Other Intangible Assets
Asset Impairments
Impairment losses										0
Solar Panels
Asset Impairments
Impairment losses							$ 0
Other Investments
Asset Impairments
Impairment losses										0
Renewables
Asset Impairments
Impairment losses									29,000,000
Construction in Progress
Asset Impairments
Impairment losses					$ 41,000,000
Construction in Progress, Gross					$ 0
Keystone
Asset Impairments
Ownership percentage	3.70%
Impairment losses on equity method investments	$ 14,000,000
Impairment losses on investments									35,000,000
Conemaugh
Asset Impairments
Impairment losses on equity method investments	$ 14,000,000
Impairment losses on investments									35,000,000
Dunkirk
Asset Impairments
Impairment losses on equity method investments				$ 46,000,000
Equity method investments				0
Other
Asset Impairments
Impairment losses on equity method investments				$ 15,000,000
Impairment losses on investments								$ 13,000,000	$ 10,000,000
South Texas Project
Asset Impairments
Impairment losses on investments			1,248,000,000
Indian River
Asset Impairments
Impairment losses on investments			$ 36,000,000
Petra Nova Parish Holdings
Asset Impairments
Ownership percentage			50.00%					50.00%				50.00%
Impairment losses on investments			$ 69,000,000			$ 140,000,000
Long Beach
Asset Impairments
Impairment losses							36,000,000
Community Wind North, LLC
Asset Impairments
Impairment losses on investments							36,000,000
Sherbino I Wind Farm LLC
Asset Impairments
Impairment losses on investments							$ 70,000,000
Rockford
Asset Impairments
Impairment losses										$ 17,000,000
Ownership percentage		100.00%
Proceeds from sale		$ 55,000,000
Held-for-sale | NRG Solar Guam, LLC
Asset Impairments
Impairment losses			$ 12,000,000
Held-for-sale | NRG Solar Guam, LLC | Subsequent Event
Asset Impairments
Cash consideration											$ 8,000,000

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- Definition

Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

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