Condensed Consolidating Financial Information (Balance Sheets) (Details 4) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014		Jun. 13, 2016	Dec. 31, 2013
Current Assets
Cash and cash equivalents		$ 1,973		$ 1,518		$ 2,116			$ 2,254
Funds deposited by counterparties		2		106
Restricted cash		446		414
Accounts receivable - trade, net		1,166		1,157
Due from Affiliate, Current		6		4
Inventory		1,111		1,252
Derivative instruments		1,062		1,915
Derivative, Collateral, Right to Reclaim Cash		203		568
Disposal Group, Including Discontinued Operation, Other Assets, Current		9		6
Prepaid Expense and Other Assets, Current Less Accounts Receivable Affiliate		417		451
Total current assets		6,395		7,391
Net Property, Plant and Equipment		17,912		18,732
Other Assets
Investment in subsidiaries		0		0
Equity investments in affiliates		1,120		1,045
Notes receivable, less current portion		17		53
Goodwill		662		999
Intangible assets, net		2,036		2,310
Nuclear decommissioning trust fund		610		561
Deferred income taxes		225		167
Derivative instruments		189		305
Disposal Group, Including Discontinued Operation, Other Assets, Noncurrent		10		105
Other non-current assets		1,179		1,214
Total other assets		6,048		6,759
Total assets		30,355		32,882
Current Liabilities
Current portion of long-term debt and capital leases		1,220		481
Accounts payable		895		869
Accounts payable - affiliate		0		0
Derivative instruments		1,084		1,721
Cash collateral received in support of energy risk management activities		2		106
Accrued interest expense		220		242
Other accrued expenses		543		568
Disposal Group, Including Discontinued Operation, Liabilities, Current		0		2
Other current liabilities		418		386
Total current liabilities		4,382		4,375
Other Liabilities
Long-term debt and capital leases		18,006		18,983
Nuclear decommissioning reserve		287		326
Nuclear decommissioning trust liability		339		283
Postretirement and other benefit obligations		553		588
Deferred income taxes		20		19
Derivative instruments		294		493
Off-market Lease, Unfavorable		1,040		1,146
Disposal Group, Including Discontinued Operation, Liabilities, Noncurrent		12		4
Other non-current liabilities		930		900
Total non-current liabilities		21,481		22,742
Total Liabilities		25,863		27,117
Redeemable noncontrolling interest in subsidiaries		0		302		291		$ 304	249
Redeemable Noncontrolling Interest, Equity, Other, Carrying Amount		46		29		19			2
Stockholders' Equity		4,446		5,434		11,676			10,467
Total Liabilities and Stockholders' Equity		30,355		32,882
Guarantor Subsidiaries
Current Assets
Cash and cash equivalents		0		0		18			56
Funds deposited by counterparties		2		55
Restricted cash		11		5
Accounts receivable - trade, net		734		851
Due from Affiliate, Current		309		395
Inventory		482		570
Derivative instruments		962		1,202
Derivative, Collateral, Right to Reclaim Cash		37		474
Disposal Group, Including Discontinued Operation, Other Assets, Current		0		0
Prepaid Expense and Other Assets, Current Less Accounts Receivable Affiliate		76		93
Total current assets		2,613		3,645
Net Property, Plant and Equipment		4,216		4,767
Other Assets
Investment in subsidiaries		837		842
Equity investments in affiliates		(14)		(14)
Notes receivable, less current portion		0		0
Goodwill		359		697
Intangible assets, net		592		763
Nuclear decommissioning trust fund		610		561
Deferred income taxes		3		(6)
Derivative instruments		143		153
Disposal Group, Including Discontinued Operation, Other Assets, Noncurrent		0		0
Other non-current assets		67		80
Total other assets		2,597		3,076
Total assets		9,426		11,488
Current Liabilities
Current portion of long-term debt and capital leases		0		2
Accounts payable		499		553
Accounts payable - affiliate		655		151
Derivative instruments		947		1,130
Cash collateral received in support of energy risk management activities		2		55
Accrued interest expense		3		5
Other accrued expenses		110		122
Disposal Group, Including Discontinued Operation, Liabilities, Current				0
Other current liabilities		204		192
Total current liabilities		2,420		2,210
Other Liabilities
Long-term debt and capital leases		244		302
Nuclear decommissioning reserve		287		326
Nuclear decommissioning trust liability		339		283
Postretirement and other benefit obligations		114		236
Deferred income taxes		186		179
Derivative instruments		157		301
Off-market Lease, Unfavorable		80		95
Disposal Group, Including Discontinued Operation, Liabilities, Noncurrent		0		0
Other non-current liabilities		283		318
Total non-current liabilities		1,690		2,040
Total Liabilities		4,110		4,250
Redeemable noncontrolling interest in subsidiaries		0		0
Redeemable Noncontrolling Interest, Equity, Other, Carrying Amount		0		0
Stockholders' Equity		5,316		7,238
Total Liabilities and Stockholders' Equity		9,426		11,488
Non-Guarantor Subsidiaries
Current Assets
Cash and cash equivalents		1,650		825		1,455			870
Funds deposited by counterparties		0		51
Restricted cash		435		409
Accounts receivable - trade, net		429		304
Due from Affiliate, Current		(241)		260
Inventory		629		682
Derivative instruments		305		871
Derivative, Collateral, Right to Reclaim Cash		166		94
Disposal Group, Including Discontinued Operation, Other Assets, Current		9		6
Prepaid Expense and Other Assets, Current Less Accounts Receivable Affiliate		279		287
Total current assets		3,661		3,789
Net Property, Plant and Equipment		13,472		13,773
Other Assets
Investment in subsidiaries		1,973		2,244
Equity investments in affiliates		1,129		1,160
Notes receivable, less current portion		17		46
Goodwill		303		302
Intangible assets, net		1,447		1,551
Nuclear decommissioning trust fund		0		0
Deferred income taxes		868		815
Derivative instruments		60		184
Disposal Group, Including Discontinued Operation, Other Assets, Noncurrent		10		105
Other non-current assets		784		749
Total other assets		6,591		7,156
Total assets		23,724		24,718
Current Liabilities
Current portion of long-term debt and capital leases		1,202		460
Accounts payable		362		277
Accounts payable - affiliate		1,834		2,000
Derivative instruments		342		749
Cash collateral received in support of energy risk management activities		0		51
Accrued interest expense		94		91
Other accrued expenses		140		151
Disposal Group, Including Discontinued Operation, Liabilities, Current				2
Other current liabilities		166		187
Total current liabilities		4,140		3,968
Other Liabilities
Long-term debt and capital leases		10,302		10,496
Nuclear decommissioning reserve		0		0
Nuclear decommissioning trust liability		0		0
Postretirement and other benefit obligations		189		200
Deferred income taxes		(1,094)		(1,088)
Derivative instruments		187		224
Off-market Lease, Unfavorable		960		1,051
Disposal Group, Including Discontinued Operation, Liabilities, Noncurrent		12		4
Other non-current liabilities		573		535
Total non-current liabilities		11,129		11,422
Total Liabilities		15,269		15,390
Redeemable noncontrolling interest in subsidiaries		0		0
Redeemable Noncontrolling Interest, Equity, Other, Carrying Amount		46		29
Stockholders' Equity		8,409		9,299
Total Liabilities and Stockholders' Equity		23,724		24,718
NRG Energy, Inc.
Current Assets
Cash and cash equivalents		323		693		$ 643			1,328
Funds deposited by counterparties		0		0
Restricted cash		0		0
Accounts receivable - trade, net		3		2
Due from Affiliate, Current		200		571
Inventory		0		0
Derivative instruments		0		0
Derivative, Collateral, Right to Reclaim Cash		0		0
Disposal Group, Including Discontinued Operation, Other Assets, Current		0		0
Prepaid Expense and Other Assets, Current Less Accounts Receivable Affiliate		62		71
Total current assets		588		1,337
Net Property, Plant and Equipment		251		219
Other Assets
Investment in subsidiaries		10,128		11,039
Equity investments in affiliates		5		1
Notes receivable, less current portion		(76)		7
Goodwill		0		0
Intangible assets, net		0		2
Nuclear decommissioning trust fund		0		0
Deferred income taxes		(646)		(642)
Derivative instruments		36		0
Disposal Group, Including Discontinued Operation, Other Assets, Noncurrent		0		0
Other non-current assets		328		385
Total other assets		9,775		10,792
Total assets		10,614		12,348
Current Liabilities
Current portion of long-term debt and capital leases		(58)		19
Accounts payable		34		39
Accounts payable - affiliate		(2,227)		(929)
Derivative instruments		0		0
Cash collateral received in support of energy risk management activities		0		0
Accrued interest expense		123		147
Other accrued expenses		293		295
Disposal Group, Including Discontinued Operation, Liabilities, Current				0
Other current liabilities		48		7
Total current liabilities		(1,787)		(422)
Other Liabilities
Long-term debt and capital leases		7,460		8,185
Nuclear decommissioning reserve		0		0
Nuclear decommissioning trust liability		0		0
Postretirement and other benefit obligations		250		152
Deferred income taxes		928		928
Derivative instruments		0		0
Off-market Lease, Unfavorable		0		0
Disposal Group, Including Discontinued Operation, Liabilities, Noncurrent		0		0
Other non-current liabilities		74		47
Total non-current liabilities		8,712		9,312
Total Liabilities		6,925		8,890
Redeemable noncontrolling interest in subsidiaries		0		302
Redeemable Noncontrolling Interest, Equity, Other, Carrying Amount		0		0
Stockholders' Equity		3,689		3,156
Total Liabilities and Stockholders' Equity		$ 10,614		$ 12,348
Convertible Preferred Stock [Member]
Condensed Financial Statements
Preferred Stock, Dividend Rate Amended, Percentage		2.822%		2.822%		2.822%
Consolidation, Eliminations [Member]
Current Assets
Cash and cash equivalents		$ 0	[1],[2]	$ 0	[2],[3],[4]	$ 0	[4],[5]		$ 0	[5]
Funds deposited by counterparties		0	[1]	0	[3]
Restricted cash		0	[1]	0	[3]
Accounts receivable - trade, net		0	[1]	0	[3]
Due from Affiliate, Current		(262)	[1]	(1,222)	[3]
Inventory		0	[1]	0	[3]
Derivative instruments		(205)	[1]	(158)	[3]
Derivative, Collateral, Right to Reclaim Cash		0	[1]	0	[3]
Disposal Group, Including Discontinued Operation, Other Assets, Current		0	[1]	0	[3]
Prepaid Expense and Other Assets, Current Less Accounts Receivable Affiliate		0	[1]	0	[3]
Total current assets		(467)	[1]	(1,380)	[3]
Net Property, Plant and Equipment		(27)	[1]	(27)	[3]
Other Assets
Investment in subsidiaries		(12,938)	[1]	(14,125)	[3]
Equity investments in affiliates		0	[1]	(102)	[3]
Notes receivable, less current portion		76	[1]	0	[3]
Goodwill		0	[1]	0	[3]
Intangible assets, net		(3)	[1]	(6)	[3]
Nuclear decommissioning trust fund		0	[1]	0	[3]
Deferred income taxes		0	[1]	0	[3]
Derivative instruments		(50)	[1]	(32)	[3]
Disposal Group, Including Discontinued Operation, Other Assets, Noncurrent		0	[1]	0	[3]
Other non-current assets		0	[1]	0	[3]
Total other assets		(12,915)	[1]	(14,265)	[3]
Total assets		(13,409)	[1]	(15,672)	[3]
Current Liabilities
Current portion of long-term debt and capital leases		76	[1]	0	[3]
Accounts payable		0	[1]	0	[3]
Accounts payable - affiliate		(262)	[1]	(1,222)	[3]
Derivative instruments		(205)	[1]	(158)	[3]
Cash collateral received in support of energy risk management activities		0	[1]	0	[3]
Accrued interest expense		0	[1]	(1)	[3]
Other accrued expenses		0	[1]	0	[3]
Disposal Group, Including Discontinued Operation, Liabilities, Current	[3]			0
Other current liabilities		0	[1]	0	[3]
Total current liabilities		(391)	[1]	(1,381)	[3]
Other Liabilities
Long-term debt and capital leases		0	[1]	0	[3]
Nuclear decommissioning reserve		0	[1]	0	[3]
Nuclear decommissioning trust liability		0	[1]	0	[3]
Postretirement and other benefit obligations		0	[1]	0	[3]
Deferred income taxes		0	[1]	0	[3]
Derivative instruments		(50)	[1]	(32)	[3]
Off-market Lease, Unfavorable		0	[1]	0	[3]
Disposal Group, Including Discontinued Operation, Liabilities, Noncurrent		0	[1]	0	[3]
Other non-current liabilities		0	[1]	0	[3]
Total non-current liabilities		(50)	[1]	(32)	[3]
Total Liabilities		(441)	[1]	(1,413)	[3]
Redeemable noncontrolling interest in subsidiaries		0	[1]	0	[3]
Redeemable Noncontrolling Interest, Equity, Other, Carrying Amount		0	[1]	0	[3]
Stockholders' Equity		(12,968)	[1]	(14,259)	[3]
Total Liabilities and Stockholders' Equity		$ (13,409)	[1]	$ (15,672)	[3]

[1] All significant intercompany transactions have been eliminated in consolidation.

[2] All significant intercompany transactions have been eliminated in consolidation.

[3] All significant intercompany transactions have been eliminated in consolidation.

[4] All significant intercompany transactions have been eliminated in consolidation.

[5] All significant intercompany transactions have been eliminated in consolidation.