Condensed Consolidating Financial Information - BALANCE SHEETS (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Current Assets
Cash and cash equivalents	$ 752	$ 938	$ 748	$ 853
Funds deposited by counterparties	19	2	1	55
Restricted cash	469	446	$ 413	$ 414
Accounts receivable - trade, net	1,162	1,058
Accounts receivable - affiliate	99	114
Inventory	713	721
Derivative instruments	644	1,067
Cash collateral paid in support of energy risk management activities	277	150
Current assets held-for-sale	33	9
Prepayments and other current assets	301	290
Current assets - discontinued operations	0	1,919
Total current assets	4,469	6,714
Net property, plant and equipment	15,302	15,369
Other Assets
Investment in subsidiaries	0	0
Equity investments in affiliates	1,127	1,120
Notes receivable, less current portion	9	16
Goodwill	662	662
Intangible assets, net	1,893	1,973
Nuclear decommissioning trust fund	637	610
Derivative instruments	226	181
Deferred income tax	211	225
Non-current assets held-for-sale	10	10
Other non-current assets	659	841
Non-current assets - discontinued operations	0	2,961
Total other assets	5,434	8,599
Total Assets	25,205	30,682
Current Liabilities
Current portion of long-term debt and capital leases	1,042	516
Accounts payable	757	782
Accounts payable - affiliate	17	31
Derivative instruments	711	1,092
Cash collateral received in support of energy risk management activities	19	81
Accrued expenses and other current liabilities	810	990
Accrued expenses and other current liabilities-affiliate	164	0
Current liabilities - discontinued operations	0	1,210
Total current liabilities	3,520	4,702
Other Liabilities
Long-term debt and capital leases	15,842	15,957
Nuclear decommissioning reserve	262	287
Nuclear decommissioning trust liability	367	339
Deferred income taxes	20	20
Derivative instruments	293	284
Out-of-market contracts, net	219	230
Non-current liabilities held-for-sale	13	11
Other non-current liabilities	1,135	1,151
Non-current liabilities - discontinued operations	0	3,209
Total non-current liabilities	18,151	21,488
Total Liabilities	21,671	26,190
Redeemable noncontrolling interest in subsidiaries	51	46
Stockholders’ Equity	3,483	4,446
Total Liabilities and Stockholders’ Equity	25,205	30,682
Eliminations
Current Assets
Cash and cash equivalents	0
Funds deposited by counterparties	0
Restricted cash	0	0
Accounts receivable - trade, net	0	0
Accounts receivable - affiliate	(102)	(139)
Inventory	0	0
Derivative instruments	(74)	(92)
Cash collateral paid in support of energy risk management activities	0	0
Current assets held-for-sale	0	0
Prepayments and other current assets	0	0
Current assets - discontinued operations		0
Total current assets	(176)	(231)
Net property, plant and equipment	(26)	(27)
Other Assets
Investment in subsidiaries	(11,824)	(12,272)
Equity investments in affiliates	0	0
Notes receivable, less current portion	0	0
Goodwill	0	0
Intangible assets, net	(3)	(3)
Nuclear decommissioning trust fund	0	0
Derivative instruments	(34)	(43)
Deferred income tax	0	0
Non-current assets held-for-sale	0	0
Other non-current assets	0	0
Non-current assets - discontinued operations		0
Total other assets	(11,861)	(12,318)
Total Assets	(12,063)	(12,576)
Current Liabilities
Current portion of long-term debt and capital leases	0	0
Accounts payable	0	0
Accounts payable - affiliate	(130)	(139)
Derivative instruments	(74)	(92)
Cash collateral received in support of energy risk management activities		0
Accrued expenses and other current liabilities	28	0
Accrued expenses and other current liabilities-affiliate	0
Current liabilities - discontinued operations		0
Total current liabilities	(176)	(231)
Other Liabilities
Long-term debt and capital leases	0	0
Nuclear decommissioning reserve	0	0
Nuclear decommissioning trust liability	0	0
Deferred income taxes	0	0
Derivative instruments	(34)	(43)
Out-of-market contracts, net	0	0
Non-current liabilities held-for-sale	0	0
Other non-current liabilities	0	0
Non-current liabilities - discontinued operations		0
Total non-current liabilities	(34)	(43)
Total Liabilities	(210)	(274)
Redeemable noncontrolling interest in subsidiaries	0	0
Stockholders’ Equity	(11,853)	(12,302)
Total Liabilities and Stockholders’ Equity	(12,063)	(12,576)
Guarantor Subsidiaries
Current Assets
Cash and cash equivalents	(19)	(9)
Funds deposited by counterparties	14	2
Restricted cash	23	11
Accounts receivable - trade, net	783	734
Accounts receivable - affiliate	195	307
Inventory	472	482
Derivative instruments	572	962
Cash collateral paid in support of energy risk management activities	252	116
Current assets held-for-sale	0	0
Prepayments and other current assets	106	76
Current assets - discontinued operations		0
Total current assets	2,398	2,681
Net property, plant and equipment	4,038	4,219
Other Assets
Investment in subsidiaries	1,158	1,090
Equity investments in affiliates	0	(13)
Notes receivable, less current portion	0	0
Goodwill	359	359
Intangible assets, net	560	592
Nuclear decommissioning trust fund	637	610
Derivative instruments	187	144
Deferred income tax	(6)	3
Non-current assets held-for-sale	0	0
Other non-current assets	60	67
Non-current assets - discontinued operations		0
Total other assets	2,955	2,852
Total Assets	9,391	9,752
Current Liabilities
Current portion of long-term debt and capital leases	0	0
Accounts payable	540	501
Accounts payable - affiliate	724	744
Derivative instruments	590	947
Cash collateral received in support of energy risk management activities	14	81
Accrued expenses and other current liabilities	298	316
Accrued expenses and other current liabilities-affiliate	0
Current liabilities - discontinued operations		0
Total current liabilities	2,166	2,589
Other Liabilities
Long-term debt and capital leases	244	244
Nuclear decommissioning reserve	262	287
Nuclear decommissioning trust liability	367	339
Deferred income taxes	308	186
Derivative instruments	179	157
Out-of-market contracts, net	74	80
Non-current liabilities held-for-sale	0	0
Other non-current liabilities	383	396
Non-current liabilities - discontinued operations		0
Total non-current liabilities	1,817	1,689
Total Liabilities	3,983	4,278
Redeemable noncontrolling interest in subsidiaries	0	0
Stockholders’ Equity	5,408	5,474
Total Liabilities and Stockholders’ Equity	9,391	9,752
Non-Guarantor Subsidiaries
Current Assets
Cash and cash equivalents	363	624
Funds deposited by counterparties	2	0
Restricted cash	443	435
Accounts receivable - trade, net	376	321
Accounts receivable - affiliate	5	(254)
Inventory	241	239
Derivative instruments	142	196
Cash collateral paid in support of energy risk management activities	25	34
Current assets held-for-sale	33	9
Prepayments and other current assets	155	152
Current assets - discontinued operations		1,919
Total current assets	1,785	3,675
Net property, plant and equipment	11,049	10,926
Other Assets
Investment in subsidiaries	1,040	1,054
Equity investments in affiliates	1,123	1,128
Notes receivable, less current portion	9	16
Goodwill	303	303
Intangible assets, net	1,336	1,384
Nuclear decommissioning trust fund	0	0
Derivative instruments	47	44
Deferred income tax	(361)	0
Non-current assets held-for-sale	10	10
Other non-current assets	537	446
Non-current assets - discontinued operations		2,961
Total other assets	4,044	7,346
Total Assets	16,878	21,947
Current Liabilities
Current portion of long-term debt and capital leases	622	498
Accounts payable	187	247
Accounts payable - affiliate	(441)	(452)
Derivative instruments	195	237
Cash collateral received in support of energy risk management activities	2	0
Accrued expenses and other current liabilities	5	209
Accrued expenses and other current liabilities-affiliate	164
Current liabilities - discontinued operations		1,210
Total current liabilities	734	1,949
Other Liabilities
Long-term debt and capital leases	8,616	8,252
Nuclear decommissioning reserve	0	0
Nuclear decommissioning trust liability	0	0
Deferred income taxes	0	125
Derivative instruments	148	170
Out-of-market contracts, net	145	150
Non-current liabilities held-for-sale	13	11
Other non-current liabilities	316	431
Non-current liabilities - discontinued operations		3,209
Total non-current liabilities	9,238	12,348
Total Liabilities	9,972	14,297
Redeemable noncontrolling interest in subsidiaries	51	46
Stockholders’ Equity	6,855	7,604
Total Liabilities and Stockholders’ Equity	16,878	21,947
NRG Energy, Inc. (Note Issuer)
Current Assets
Cash and cash equivalents	408	323
Funds deposited by counterparties	3	0
Restricted cash	3	0
Accounts receivable - trade, net	3	3
Accounts receivable - affiliate	1	200
Inventory	0	0
Derivative instruments	4	1
Cash collateral paid in support of energy risk management activities	0	0
Current assets held-for-sale	0	0
Prepayments and other current assets	40	62
Current assets - discontinued operations		0
Total current assets	462	589
Net property, plant and equipment	241	251
Other Assets
Investment in subsidiaries	9,626	10,128
Equity investments in affiliates	4	5
Notes receivable, less current portion	0	0
Goodwill	0	0
Intangible assets, net	0	0
Nuclear decommissioning trust fund	0	0
Derivative instruments	26	36
Deferred income tax	578	222
Non-current assets held-for-sale	0	0
Other non-current assets	62	328
Non-current assets - discontinued operations		0
Total other assets	10,296	10,719
Total Assets	10,999	11,559
Current Liabilities
Current portion of long-term debt and capital leases	420	18
Accounts payable	30	34
Accounts payable - affiliate	(136)	(122)
Derivative instruments	0	0
Cash collateral received in support of energy risk management activities	3	0
Accrued expenses and other current liabilities	479	465
Accrued expenses and other current liabilities-affiliate	0
Current liabilities - discontinued operations		0
Total current liabilities	796	395
Other Liabilities
Long-term debt and capital leases	6,982	7,461
Nuclear decommissioning reserve	0	0
Nuclear decommissioning trust liability	0	0
Deferred income taxes	(288)	(291)
Derivative instruments	0	0
Out-of-market contracts, net	0	0
Non-current liabilities held-for-sale	0	0
Other non-current liabilities	436	324
Non-current liabilities - discontinued operations		0
Total non-current liabilities	7,130	7,494
Total Liabilities	7,926	7,889
Redeemable noncontrolling interest in subsidiaries	0	0
Stockholders’ Equity	3,073	3,670
Total Liabilities and Stockholders’ Equity	$ 10,999	$ 11,559