Condensed Consolidating Financial Information - CONSOLIDATING BALANCE SHEETS (Details) - USD ($) $ in Millions	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Current Assets
Cash and cash equivalents	$ 294		$ 563
Funds deposited by counterparties	31		33
Restricted cash	11		17
Accounts receivable, net	1,049		1,024
Inventory	370		412
Derivative instruments	850		764
Cash collateral paid in support of energy risk management activities	163		287
Prepayments and other current assets	277		302
Current assets - held-for-sale	0		1
Current assets - discontinued operations	0		197
Total current assets	3,045		3,600
Property, plant and equipment, net	2,610		3,048
Other Assets
Investment in subsidiaries	0		0
Equity investments in affiliates	383		412
Operating lease right-of-use assets, net	499
Goodwill	573		573
Intangible assets, net	561		591
Nuclear decommissioning trust fund	748		663
Derivative instruments	426		317
Deferred income tax	55		46
Other non-current assets	271		289
Non-current assets - held-for-sale	0		77
Non-current assets - discontinued operations	0		1,012
Total other assets	3,516		3,980
Total Assets	9,171		10,628
Current Liabilities
Current portion of long-term debt and capital leases	87		72
Current portion of operating lease liabilities	74
Accounts payable	723		863
Derivative instruments	778		673
Cash collateral received in support of energy risk management activities	31		33
Accrued expenses and other current liabilities	601		680
Current liabilities - held-for-sale	0		5
Current liabilities - discontinued operations	0		72
Total current liabilities	2,294		2,398
Other Liabilities
Long-term debt and capital leases	5,794		6,449
Non-current operating lease liabilities	513
Nuclear decommissioning reserve	290		282
Nuclear decommissioning trust liability	448		371
Derivative instruments	374		304
Deferred income taxes	71		65
Other non-current liabilities	1,016		1,274
Non-current liabilities - held-for-sale	0		65
Non-current liabilities - discontinued operations	0		635
Total other liabilities	8,506		9,445
Total Liabilities	10,800		11,843
Redeemable noncontrolling interest in subsidiaries	19		19
Total Stockholders' Equity	(1,648)	$ (1,538)	(1,234)	$ 2,071	$ 2,258	$ 1,968
Total Liabilities and Stockholders' Equity	9,171		10,628
Eliminations
Current Assets
Cash and cash equivalents	0		0
Funds deposited by counterparties	0		0
Restricted cash	0		0
Accounts receivable, net	(744)		(754)
Inventory	0		0
Derivative instruments	(71)		(81)
Cash collateral paid in support of energy risk management activities	0		0
Prepayments and other current assets	0		0
Current assets - held-for-sale			0
Current assets - discontinued operations			0
Total current assets	(815)		(835)
Property, plant and equipment, net	0		0
Other Assets
Investment in subsidiaries	(4,627)		(5,153)
Equity investments in affiliates	0		0
Operating lease right-of-use assets, net	0
Goodwill	0		0
Intangible assets, net	0		0
Nuclear decommissioning trust fund	0		0
Derivative instruments	(16)		(5)
Deferred income tax	0		0
Other non-current assets	(3)		(12)
Non-current assets - held-for-sale			0
Non-current assets - discontinued operations			0
Total other assets	(4,646)		(5,170)
Total Assets	(5,461)		(6,005)
Current Liabilities
Current portion of long-term debt and capital leases	0		0
Current portion of operating lease liabilities	0
Accounts payable	(744)		(754)
Derivative instruments	(71)		(81)
Cash collateral received in support of energy risk management activities	0		0
Accrued expenses and other current liabilities	0		0
Current liabilities - held-for-sale			0
Current liabilities - discontinued operations			0
Total current liabilities	(815)		(835)
Other Liabilities
Long-term debt and capital leases	(3)		(12)
Non-current operating lease liabilities	0
Nuclear decommissioning reserve	0		0
Nuclear decommissioning trust liability	0		0
Derivative instruments	(16)		(5)
Deferred income taxes	0		0
Other non-current liabilities	0		0
Non-current liabilities - held-for-sale			0
Non-current liabilities - discontinued operations			0
Total other liabilities	(19)		(17)
Total Liabilities	(834)		(852)
Redeemable noncontrolling interest in subsidiaries	0		0
Total Stockholders' Equity	(4,627)		(5,153)
Total Liabilities and Stockholders' Equity	(5,461)		(6,005)
Guarantor Subsidiaries
Current Assets
Cash and cash equivalents	0		55
Funds deposited by counterparties	31		33
Restricted cash	8		7
Accounts receivable, net	1,383		1,354
Inventory	254		278
Derivative instruments	867		779
Cash collateral paid in support of energy risk management activities	148		275
Prepayments and other current assets	190		180
Current assets - held-for-sale			0
Current assets - discontinued operations			177
Total current assets	2,881		3,138
Property, plant and equipment, net	1,494		1,938
Other Assets
Investment in subsidiaries	436		446
Equity investments in affiliates	0		0
Operating lease right-of-use assets, net	91
Goodwill	359		359
Intangible assets, net	402		422
Nuclear decommissioning trust fund	748		663
Derivative instruments	420		296
Deferred income tax	0		6
Other non-current assets	148		133
Non-current assets - held-for-sale			0
Non-current assets - discontinued operations			405
Total other assets	2,604		2,730
Total Assets	6,979		7,806
Current Liabilities
Current portion of long-term debt and capital leases	0		0
Current portion of operating lease liabilities	22
Accounts payable	937		1,368
Derivative instruments	817		713
Cash collateral received in support of energy risk management activities	31		33
Accrued expenses and other current liabilities	258		291
Current liabilities - held-for-sale			0
Current liabilities - discontinued operations			24
Total current liabilities	2,065		2,429
Other Liabilities
Long-term debt and capital leases	245		244
Non-current operating lease liabilities	73
Nuclear decommissioning reserve	290		282
Nuclear decommissioning trust liability	448		371
Derivative instruments	388		306
Deferred income taxes	(10)		112
Other non-current liabilities	399		402
Non-current liabilities - held-for-sale			0
Non-current liabilities - discontinued operations			58
Total other liabilities	1,833		1,775
Total Liabilities	3,898		4,204
Redeemable noncontrolling interest in subsidiaries	0		0
Total Stockholders' Equity	3,081		3,602
Total Liabilities and Stockholders' Equity	6,979		7,806
Non-Guarantor Subsidiaries
Current Assets
Cash and cash equivalents	27		28
Funds deposited by counterparties	0		0
Restricted cash	2		10
Accounts receivable, net	133		115
Inventory	116		134
Derivative instruments	54		50
Cash collateral paid in support of energy risk management activities	15		12
Prepayments and other current assets	11		32
Current assets - held-for-sale			1
Current assets - discontinued operations			20
Total current assets	358		402
Property, plant and equipment, net	965		957
Other Assets
Investment in subsidiaries	0		0
Equity investments in affiliates	383		412
Operating lease right-of-use assets, net	279
Goodwill	214		214
Intangible assets, net	159		169
Nuclear decommissioning trust fund	0		0
Derivative instruments	22		4
Deferred income tax	56		(143)
Other non-current assets	30		71
Non-current assets - held-for-sale			77
Non-current assets - discontinued operations			607
Total other assets	1,143		1,411
Total Assets	2,466		2,770
Current Liabilities
Current portion of long-term debt and capital leases	87		55
Current portion of operating lease liabilities	31
Accounts payable	107		(185)
Derivative instruments	32		41
Cash collateral received in support of energy risk management activities	0		0
Accrued expenses and other current liabilities	42		36
Current liabilities - held-for-sale			5
Current liabilities - discontinued operations			48
Total current liabilities	299		0
Other Liabilities
Long-term debt and capital leases	89		192
Non-current operating lease liabilities	313
Nuclear decommissioning reserve	0		0
Nuclear decommissioning trust liability	0		0
Derivative instruments	2		3
Deferred income taxes	68		61
Other non-current liabilities	148		320
Non-current liabilities - held-for-sale			65
Non-current liabilities - discontinued operations			577
Total other liabilities	620		1,218
Total Liabilities	919		1,218
Redeemable noncontrolling interest in subsidiaries	19		19
Total Stockholders' Equity	1,528		1,533
Total Liabilities and Stockholders' Equity	2,466		2,770
NRG Energy, Inc. (Note Issuer)
Current Assets
Cash and cash equivalents	267		480
Funds deposited by counterparties	0		0
Restricted cash	1		0
Accounts receivable, net	277		309
Inventory	0		0
Derivative instruments	0		16
Cash collateral paid in support of energy risk management activities	0		0
Prepayments and other current assets	76		90
Current assets - held-for-sale			0
Current assets - discontinued operations			0
Total current assets	621		895
Property, plant and equipment, net	151		153
Other Assets
Investment in subsidiaries	4,191		4,707
Equity investments in affiliates	0		0
Operating lease right-of-use assets, net	129
Goodwill	0		0
Intangible assets, net	0		0
Nuclear decommissioning trust fund	0		0
Derivative instruments	0		22
Deferred income tax	(1)		183
Other non-current assets	96		97
Non-current assets - held-for-sale			0
Non-current assets - discontinued operations			0
Total other assets	4,415		5,009
Total Assets	5,187		6,057
Current Liabilities
Current portion of long-term debt and capital leases	0		17
Current portion of operating lease liabilities	21
Accounts payable	423		434
Derivative instruments	0		0
Cash collateral received in support of energy risk management activities	0		0
Accrued expenses and other current liabilities	301		353
Current liabilities - held-for-sale			0
Current liabilities - discontinued operations			0
Total current liabilities	745		804
Other Liabilities
Long-term debt and capital leases	5,463		6,025
Non-current operating lease liabilities	127
Nuclear decommissioning reserve	0		0
Nuclear decommissioning trust liability	0		0
Derivative instruments	0		0
Deferred income taxes	13		(108)
Other non-current liabilities	469		552
Non-current liabilities - held-for-sale			0
Non-current liabilities - discontinued operations			0
Total other liabilities	6,072		6,469
Total Liabilities	6,817		7,273
Redeemable noncontrolling interest in subsidiaries	0		0
Total Stockholders' Equity	(1,630)		(1,216)
Total Liabilities and Stockholders' Equity	$ 5,187		$ 6,057