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Debt and Capital Leases - Schedule of Long-term Debt and Capital Leases (Details) - USD ($) $ in Millions				12 Months Ended
	Mar. 21, 2018	Jan. 24, 2017	Jun. 30, 2016	Dec. 31, 2018	Nov. 05, 2018	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Dec. 07, 2017
Debt Instrument [Line Items]
Long-term debt				$ 6,691				$ 9,494
Capital leases				1				5
Subtotal				6,692				9,499
Less current maturities				(72)				(204)
Less debt issuance costs				(70)				(103)
Discounts				(101)				(12)
Total long-term debt and capital leases				6,449				9,180
Debt Instrument, Unamortized Discount [Abstract]
Total discounts				(101)				(12)
Recourse Debt
Debt Instrument [Line Items]
Long-term debt				6,523				7,182
Recourse Debt \| Senior notes, due 2022
Debt Instrument [Line Items]
Long-term debt				$ 0				992
Interest rate, stated percentage				6.25%		6.25%	6.25%
Recourse Debt \| Senior notes, due 2024
Debt Instrument [Line Items]
Long-term debt				$ 733				733
Interest rate, stated percentage				6.25%		6.25%
Recourse Debt \| Senior notes, due 2026
Debt Instrument [Line Items]
Long-term debt				$ 1,000				1,000
Interest rate, stated percentage				7.25%		7.25%
Recourse Debt \| Senior notes, due 2027
Debt Instrument [Line Items]
Long-term debt				$ 1,230				1,250
Interest rate, stated percentage				6.625%		6.625%
Recourse Debt \| Senior notes, due 2028
Debt Instrument [Line Items]
Long-term debt				$ 821				870
Interest rate, stated percentage				5.75%		5.75%	5.75%		5.75%
Recourse Debt \| Convertible Senior Notes, due 2048
Debt Instrument [Line Items]
Long-term debt				$ 575				0
Interest rate, stated percentage						2.75%
Debt Instrument, Unamortized Discount [Abstract]
Unamortized discount on debt instruments				(96)				0
Recourse Debt \| Term loan facility, due 2023
Debt Instrument [Line Items]
Long-term debt			$ 1,900	1,698	$ 260			1,872
Debt Instrument, Unamortized Discount [Abstract]
Unamortized discount on debt instruments				$ (4)				(7)
Recourse Debt \| Term loan facility, due 2023 \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	1.75%	2.25%	2.75%	1.75%
Recourse Debt \| Tax-exempt bonds
Debt Instrument [Line Items]
Long-term debt				$ 466				465
Recourse Debt \| Tax-exempt bonds \| Low
Debt Instrument [Line Items]
Interest rate, stated percentage				4.125%
Recourse Debt \| Tax-exempt bonds \| Maximum
Debt Instrument [Line Items]
Interest rate, stated percentage				6.00%
Non Recourse Debt
Debt Instrument [Line Items]
Long-term debt				$ 168				2,312
Non Recourse Debt \| Ivanpah, due 2033 and 2038
Debt Instrument [Line Items]
Long-term debt				$ 0				1,073
Non Recourse Debt \| Ivanpah, due 2033 and 2038 \| Low
Debt Instrument [Line Items]
Interest rate, stated percentage				2.285%
Non Recourse Debt \| Ivanpah, due 2033 and 2038 \| Maximum
Debt Instrument [Line Items]
Interest rate, stated percentage				4.256%
Non Recourse Debt \| Agua Caliente, due 2037
Debt Instrument [Line Items]
Long-term debt				$ 0				818
Non Recourse Debt \| Agua Caliente, due 2037 \| Low
Debt Instrument [Line Items]
Interest rate, stated percentage				2.395%
Non Recourse Debt \| Agua Caliente, due 2037 \| Maximum
Debt Instrument [Line Items]
Interest rate, stated percentage				3.633%
Non Recourse Debt \| Agua Caliente Borrower 1, due 2038
Debt Instrument [Line Items]
Long-term debt				$ 86				89
Interest rate, stated percentage						5.43%
Non Recourse Debt \| Midwest Generation, due 2019
Debt Instrument [Line Items]
Long-term debt				48				152
Interest rate, stated percentage						4.39%
Debt Instrument, Unamortized Discount [Abstract]
Unamortized discount on debt instruments				(1)				(5)
Non Recourse Debt \| NRG Other
Debt Instrument [Line Items]
Long-term debt				$ 34				$ 180