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Summary of Significant Accounting Policies - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 1,823
Unrealized Gain (Loss) on Derivatives, Mark To Market, Economic Hedging Activities	196	$ (19)
Derivative revenue	204	(33)
Contract amortization	(14)
Operating revenues	2,421	2,382
Lease revenue	252
Eliminations
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(182)
Contract amortization	0
Operating revenues	300	(244)
Lease revenue	0
Energy revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	619
Derivative revenue	432
Lease revenue	163
Energy revenue | Eliminations
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(161)
Derivative revenue	0
Lease revenue	0
Capacity revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	288
Derivative revenue	26
Lease revenue	79
Capacity revenue | Eliminations
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(1)
Derivative revenue	0
Lease revenue	0
Retail
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers
Retail | Eliminations
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers
Retail | Mass customers
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,170
Retail | Mass customers | Eliminations
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(1)
Retail | Business solutions customers
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	316
Retail | Business solutions customers | Eliminations
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0
Total retail revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,486
Total retail revenue | Eliminations
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(1)
Derivative revenue
Disaggregation of Revenue [Line Items]
Unrealized Gain (Loss) on Derivatives, Mark To Market, Economic Hedging Activities	(106)
Derivative revenue	360
Derivative revenue | Eliminations
Disaggregation of Revenue [Line Items]
Unrealized Gain (Loss) on Derivatives, Mark To Market, Economic Hedging Activities	484
Derivative revenue	484
Other revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	148
Lease revenue	10
Other revenue | Eliminations
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	(19)
Lease revenue	0
Total operating revenue
Disaggregation of Revenue [Line Items]
Operating revenues	2,421
Total operating revenue | Eliminations
Disaggregation of Revenue [Line Items]
Operating revenues	302
Other derivative revenue
Disaggregation of Revenue [Line Items]
Derivative revenue	8
Other derivative revenue | Eliminations
Disaggregation of Revenue [Line Items]
Derivative revenue	0
Retail | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,481
Contract amortization	0
Operating revenues	1,481	1,335
Lease revenue	6
Retail | Eliminations
Disaggregation of Revenue [Line Items]
Operating revenues	(1)	(1)
Retail | Energy revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0
Derivative revenue	0
Lease revenue	0
Retail | Capacity revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0
Derivative revenue	0
Lease revenue	0
Retail | Retail | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers
Retail | Retail | Mass customers | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,171
Retail | Retail | Business solutions customers | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	316
Retail | Total retail revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,487
Retail | Derivative revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Unrealized Gain (Loss) on Derivatives, Mark To Market, Economic Hedging Activities	(6)
Derivative revenue	(6)
Retail | Other revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0
Lease revenue	6
Retail | Total operating revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Operating revenues	1,481
Retail | Other derivative revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Derivative revenue	0
Generation | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	431
Contract amortization	3
Operating revenues	327	965
Lease revenue	1
Generation | Eliminations
Disaggregation of Revenue [Line Items]
Operating revenues	307	(209)
Generation | Energy revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	589
Derivative revenue	432
Lease revenue	0
Generation | Capacity revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	207
Derivative revenue	26
Lease revenue	0
Generation | Retail | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers
Generation | Retail | Mass customers | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0
Generation | Retail | Business solutions customers | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0
Generation | Total retail revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0
Generation | Derivative revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Unrealized Gain (Loss) on Derivatives, Mark To Market, Economic Hedging Activities	(574)
Derivative revenue	(108)
Generation | Other revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	102
Lease revenue	1
Generation | Total operating revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Operating revenues	327
Generation | Other derivative revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Derivative revenue	8
Generation | Gulf Coast | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	148
Contract amortization	3
Lease revenue	0
Generation | Gulf Coast | Energy revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	371
Derivative revenue	371
Lease revenue	0
Generation | Gulf Coast | Capacity revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	67
Derivative revenue	0
Lease revenue	0
Generation | Gulf Coast | Retail | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers
Generation | Gulf Coast | Retail | Mass customers | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0
Generation | Gulf Coast | Retail | Business solutions customers | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0
Generation | Gulf Coast | Total retail revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0
Generation | Gulf Coast | Derivative revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Unrealized Gain (Loss) on Derivatives, Mark To Market, Economic Hedging Activities	(564)
Derivative revenue	(188)
Generation | Gulf Coast | Other revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	86
Lease revenue	0
Generation | Gulf Coast | Total operating revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Operating revenues	(37)
Generation | Gulf Coast | Other derivative revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Derivative revenue	5
Generation | East and West | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	283
Contract amortization	0
Lease revenue	1
Generation | East and West | Energy revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	218
Derivative revenue	61
Lease revenue	0
Generation | East and West | Capacity revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	140
Derivative revenue	26
Lease revenue	0
Generation | East and West | Retail | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers
Generation | East and West | Retail | Mass customers | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0
Generation | East and West | Retail | Business solutions customers | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0
Generation | East and West | Total retail revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0
Generation | East and West | Derivative revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Unrealized Gain (Loss) on Derivatives, Mark To Market, Economic Hedging Activities	(10)
Derivative revenue	80
Generation | East and West | Other revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	16
Lease revenue	1
Generation | East and West | Total operating revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Operating revenues	364
Generation | East and West | Other derivative revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Derivative revenue	3
Renewables | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	32
Contract amortization	0
Operating revenues	86	95
Lease revenue	64
Renewables | Eliminations
Disaggregation of Revenue [Line Items]
Operating revenues	(8)	(8)
Renewables | Energy revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	77
Derivative revenue	0
Lease revenue	61
Renewables | Capacity revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0
Derivative revenue	0
Lease revenue	0
Renewables | Retail | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers
Renewables | Retail | Mass customers | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0
Renewables | Retail | Business solutions customers | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0
Renewables | Total retail revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0
Renewables | Derivative revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Unrealized Gain (Loss) on Derivatives, Mark To Market, Economic Hedging Activities	(10)
Derivative revenue	(10)
Renewables | Other revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	19
Lease revenue	3
Renewables | Total operating revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Operating revenues	86
Renewables | Other derivative revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Derivative revenue	0
NRG Yield | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	61
Contract amortization	(17)
Operating revenues	225	221
Lease revenue	181
NRG Yield | Eliminations
Disaggregation of Revenue [Line Items]
Operating revenues	0	$ 0
NRG Yield | Energy revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	114
Derivative revenue	0
Lease revenue	102
NRG Yield | Capacity revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	82
Derivative revenue	0
Lease revenue	79
NRG Yield | Retail | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers
NRG Yield | Retail | Mass customers | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0
NRG Yield | Retail | Business solutions customers | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0
NRG Yield | Total retail revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0
NRG Yield | Derivative revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Unrealized Gain (Loss) on Derivatives, Mark To Market, Economic Hedging Activities	0
Derivative revenue	0
NRG Yield | Other revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	46
Lease revenue	0
NRG Yield | Total operating revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Operating revenues	225
NRG Yield | Other derivative revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Derivative revenue	$ 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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