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Summary of Significant Accounting Policies - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 1,928		$ 3,751
Mark-to-market for economic hedging activities	(71)	$ 59	125	$ 41
Contract amortization	(14)		(28)
Operating revenues	2,922	2,701	5,343	5,083
Lease revenue	370		622
Derivative revenue	(66)	71	138	39
Eliminations
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(269)		(451)
Contract amortization	0		0
Operating revenues	(540)	(194)	(240)	(436)
Lease revenue	0		0
Energy revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	673		1,292
Lease revenue	272		435
Derivative revenue	580		1,012
Energy revenue | Eliminations
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(250)		(411)
Lease revenue	0		0
Derivative revenue	0		0
Capacity revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	313		601
Lease revenue	85		164
Derivative revenue	39		65
Capacity revenue | Eliminations
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(2)		(3)
Lease revenue	0		0
Derivative revenue	0		0
Retail revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers
Retail revenue | Eliminations
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers
Retail revenue | Mass customers
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,379		2,549
Retail revenue | Mass customers | Eliminations
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(1)		(2)
Retail revenue | Business solutions customers
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	437		753
Retail revenue | Business solutions customers | Eliminations
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0		0
Total retail revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,816		3,302
Total retail revenue | Eliminations
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(1)		(2)
Derivative revenue
Disaggregation of Revenue [Line Items]
Mark-to-market for economic hedging activities	15		(91)
Derivative revenue	638		998
Derivative revenue | Eliminations
Disaggregation of Revenue [Line Items]
Mark-to-market for economic hedging activities	(264)		220
Derivative revenue	(264)		220
Other revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	119		267
Lease revenue	13		23
Other revenue | Eliminations
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(16)		(35)
Lease revenue	0		0
Total operating revenue
Disaggregation of Revenue [Line Items]
Operating revenues	2,922		5,343
Total operating revenue | Eliminations
Disaggregation of Revenue [Line Items]
Operating revenues	(533)		(231)
Other derivative revenue
Disaggregation of Revenue [Line Items]
Derivative revenue	4		12
Other derivative revenue | Eliminations
Disaggregation of Revenue [Line Items]
Derivative revenue	0		0
Retail | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,811		3,292
Contract amortization	0		0
Operating revenues	1,817	1,603	3,298	2,938
Lease revenue	6		12
Retail | Eliminations
Disaggregation of Revenue [Line Items]
Operating revenues	(2)	(1)	(3)	(11)
Retail | Energy revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0		0
Lease revenue	0		0
Derivative revenue	0		0
Retail | Capacity revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0		0
Lease revenue	0		0
Derivative revenue	0		0
Retail | Retail revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers
Retail | Retail revenue | Mass customers | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,380		2,551
Retail | Retail revenue | Business solutions customers | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	437		753
Retail | Total retail revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,817		3,304
Retail | Derivative revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Mark-to-market for economic hedging activities	0		(6)
Derivative revenue	0		(6)
Retail | Other revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0		0
Lease revenue	6		12
Retail | Total operating revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Operating revenues	1,817		3,298
Retail | Other derivative revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Derivative revenue	0		0
Generation | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	316		747
Contract amortization	4		7
Operating revenues	1,218	882	1,545	1,848
Lease revenue	1		2
Generation | Eliminations
Disaggregation of Revenue [Line Items]
Operating revenues	(546)	(171)	(239)	(406)
Generation | Energy revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	652		1,241
Lease revenue	0		0
Derivative revenue	580		1,012
Generation | Capacity revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	228		435
Lease revenue	0		0
Derivative revenue	39		65
Generation | Retail revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers
Generation | Retail revenue | Mass customers | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0		0
Generation | Retail revenue | Business solutions customers | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0		0
Generation | Total retail revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0		0
Generation | Derivative revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Mark-to-market for economic hedging activities	274		(300)
Derivative revenue	897		789
Generation | Other revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	60		162
Lease revenue	1		2
Generation | Total operating revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Operating revenues	1,218		1,545
Generation | Other derivative revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Derivative revenue	4		12
Generation | Gulf Coast | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	9		157
Contract amortization	4		7
Lease revenue	0		0
Generation | Gulf Coast | Energy revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	508		879
Lease revenue	0		0
Derivative revenue	610		981
Generation | Gulf Coast | Capacity revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	68		135
Lease revenue	0		0
Derivative revenue	0		0
Generation | Gulf Coast | Retail revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers
Generation | Gulf Coast | Retail revenue | Mass customers | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0		0
Generation | Gulf Coast | Retail revenue | Business solutions customers | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0		0
Generation | Gulf Coast | Total retail revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0		0
Generation | Gulf Coast | Derivative revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Mark-to-market for economic hedging activities	289		(275)
Derivative revenue	898		710
Generation | Gulf Coast | Other revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	42		128
Lease revenue	0		0
Generation | Gulf Coast | Total operating revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Operating revenues	911		874
Generation | Gulf Coast | Other derivative revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Derivative revenue	(1)		4
Generation | East and West | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	307		590
Contract amortization	0		0
Lease revenue	1		2
Generation | East and West | Energy revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	144		362
Lease revenue	0		0
Derivative revenue	(30)		31
Generation | East and West | Capacity revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	160		300
Lease revenue	0		0
Derivative revenue	39		65
Generation | East and West | Retail revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers
Generation | East and West | Retail revenue | Mass customers | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0		0
Generation | East and West | Retail revenue | Business solutions customers | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0		0
Generation | East and West | Total retail revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0		0
Generation | East and West | Derivative revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Mark-to-market for economic hedging activities	(15)		(25)
Derivative revenue	(1)		79
Generation | East and West | Other revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	18		34
Lease revenue	1		2
Generation | East and West | Total operating revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Operating revenues	307		671
Generation | East and West | Other derivative revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Derivative revenue	5		8
Renewables | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	12		44
Contract amortization	0		0
Operating revenues	113	119	199	213
Lease revenue	96		160
Renewables | Eliminations
Disaggregation of Revenue [Line Items]
Operating revenues	(9)	(3)	(17)	(4)
Renewables | Energy revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	79		156
Lease revenue	90		151
Derivative revenue	0		0
Renewables | Capacity revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0		0
Lease revenue	0		0
Derivative revenue	0		0
Renewables | Retail revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers
Renewables | Retail revenue | Mass customers | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0		0
Renewables | Retail revenue | Business solutions customers | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0		0
Renewables | Total retail revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0		0
Renewables | Derivative revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Mark-to-market for economic hedging activities	5		(5)
Derivative revenue	5		(5)
Renewables | Other revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	29		48
Lease revenue	6		9
Renewables | Total operating revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Operating revenues	113		199
Renewables | Other derivative revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Derivative revenue	0		0
NRG Yield | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	58		119
Contract amortization	(18)		(35)
Operating revenues	307	288	532	509
Lease revenue	267		448
NRG Yield | Eliminations
Disaggregation of Revenue [Line Items]
Operating revenues	0	$ 0	0	$ 0
NRG Yield | Energy revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	192		306
Lease revenue	182		284
Derivative revenue	0		0
NRG Yield | Capacity revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	87		169
Lease revenue	85		164
Derivative revenue	0		0
NRG Yield | Retail revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers
NRG Yield | Retail revenue | Mass customers | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0		0
NRG Yield | Retail revenue | Business solutions customers | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0		0
NRG Yield | Total retail revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0		0
NRG Yield | Derivative revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Mark-to-market for economic hedging activities	0		0
Derivative revenue	0		0
NRG Yield | Other revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	46		92
Lease revenue	0		0
NRG Yield | Total operating revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Operating revenues	307		532
NRG Yield | Other derivative revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Derivative revenue	$ 0		$ 0

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Amount of amortization expense for asset recognized from cost incurred to obtain or fulfill contract with customer.

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Amount of contingent rental revenue recognized for the period under lease, based on the occurrences of an event or condition.

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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