Accounting for Derivative Instruments and Hedging Activities (Tables)

12 Months Ended

Dec. 31, 2017

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Net Notional Volume Buy/(sell) of NRG's Open Derivative Transactions Broken Out By Commodity

The following table summarizes the net notional volume buy/(sell) of NRG's open derivative transactions broken out by commodity, excluding those derivatives that qualified for the NPNS exception as of December 31, 2017 and 2016. Option contracts are reflected using delta volume. Delta volume equals the notional volume of an option adjusted for the probability that the option will be in-the-money at its expiration date.



		Total Volume
Commodity	Units	December 31, 2017			December 31, 2016
		(In millions)
Emissions	Short Ton	1			—
Coal	Short Ton	21			35
Natural Gas	MMBtu	(17		)	(53		)
Oil	Barrel	—			1
Power	MWh	14			7
Capacity	MW/Day	(1		)	(1		)
Interest	Dollars	$	3,876		$	3,429
Equity	Shares	1			1

Fair Value Within the Derivative Instrument Valuation On the Balance Sheets

The following table summarizes the fair value within the derivative instrument valuation on the balance sheet:



	Fair Value
	Derivative Assets				Derivative Liabilities
(In millions)	December 31, 2017		December 31, 2016		December 31, 2017		December 31, 2016
Derivatives Designated as Cash Flow or Fair Value Hedges:
Interest rate contracts current	$	1	$	—	$	5	$	28
Interest rate contracts long-term	11		12		11		41
Total Derivatives Designated as Cash Flow or Fair Value Hedges	12		12		16		69
Derivatives Not Designated as Cash Flow or Fair Value Hedges:
Interest rate contracts current	9		—		15		7
Interest rate contracts long-term	32		37		28		12
Commodity contracts current	616		1,067		535		1,057
Commodity contracts long-term	129		132		158		231
Total Derivatives Not Designated as Cash Flow or Fair Value Hedges	786		1,236		736		1,307
Total Derivatives	$	798	$	1,248	$	752	$	1,376

Offsetting of Derivatives by Counterparty Master Agreement Level and Collateral Received Or Paid

The following table summarizes the offsetting derivatives by counterparty master agreement level and collateral received or paid:



	Gross Amounts Not Offset in the Statement of Financial Position
	Gross Amounts of Recognized Assets/Liabilities			Derivative Instruments			Cash Collateral (Held)/Posted			Net Amount
As of December 31, 2017	(In millions)
Commodity contracts:
Derivative assets	$	745		$	(578	)	$	(11	)	$	156
Derivative liabilities	(693		)	578			73			(42		)
Total commodity contracts	52			—			62			114
Interest rate contracts:
Derivative assets	53			(3		)	—			50
Derivative liabilities	(59		)	3			—			(56		)
Total interest rate contracts	(6		)	—			—			(6		)
Total derivative instruments	$	46		$	—		$	62		$	108



	Gross Amounts Not Offset in the Statement of Financial Position
	Gross Amounts of Recognized Assets/Liabilities			Derivative Instruments			Cash Collateral (Held)/Posted			Net Amount
As of December 31, 2016	(In millions)
Commodity contracts:
Derivative assets	$	1,199		$	(1,021	)	$	(13	)	$	165
Derivative liabilities	(1,288		)	1,021			13			(254		)
Total commodity contracts	(89		)	—			—			(89		)
Interest rate contracts:
Derivative assets	49			(4		)				45
Derivative liabilities	(88		)	4			—			(84		)
Total interest rate contracts	(39		)	—			—			(39		)
Total derivative instruments	$	(128	)	$	—		$	—		$	(128	)

Effects of ASC 815 on the Company's Accumulated OCI Balance Attributable to Cash Flow Hedge Derivatives, Net of Tax

The following tables summarize the effects on NRG's accumulated OCI balance attributable to cash flow hedge derivatives, net of tax:



	Year Ended December 31, 2017
	Interest Rate			Total
	(In millions)
Accumulated OCI balance at December 31, 2016	$	(66	)	$	(66	)
Reclassified from accumulated OCI to income:
Due to realization of previously deferred amounts	12			12
Mark-to-market of cash flow hedge accounting contracts	—			—
Accumulated OCI balance at December 31, 2017, net of $8 tax	$	(54	)	$	(54	)
Losses expected to be realized from other comprehensive loss during the next 12 months, net of $2 tax	$	(12	)	$	(12	)



	Year Ended December 31, 2016
	Interest Rate			Total
	(In millions)
Accumulated OCI balance at December 31, 2015	$	(101	)	$	(101	)
Reclassified from accumulated OCI to income:
Due to realization of previously deferred amounts	21			21
Mark-to-market of cash flow hedge accounting contracts	14			14
Accumulated OCI balance at December 31, 2016, net of $16 tax	$	(66	)	$	(66	)



	Year Ended December 31, 2015
	Energy Commodities			Interest Rate			Total
	(In millions)
Accumulated OCI balance at December 31, 2014	$	(1	)	$	(67	)	$	(68	)
Reclassified from accumulated OCI to income:
Due to realization of previously deferred amounts	1			14			15
Mark-to-market of cash flow hedge accounting contracts	—			(48		)	(48		)
Accumulated OCI balance at December 31, 2015, net of $16 tax	$	—		$	(101	)	$	(101	)

Pre-tax Effects of Economic Hedges That Have Not Been Designated As Cash Flow Hedges, Ineffectiveness On Cash Flow Hedges And Trading Activity on the Company's Statement of Operations

The following table summarizes the pre-tax effects of economic hedges that have not been designated as cash flow hedges, and trading activity on the Company's statement of operations. The effect of commodity hedges is included within operating revenues and cost of operations and the effect of interest rate hedges is included in interest expense.



	Year Ended December 31,
	2017			2016			2015
	(In millions)
Unrealized mark-to-market results
Reversal of previously recognized unrealized loss/(gains) on settled positions related to economic hedges	$	47		$	(128	)	$	(162	)
Reversal of acquired gain positions related to economic hedges	—			(12		)	(22		)
Net unrealized gains/(losses) on open positions related to economic hedges	146			6			(9		)
Total unrealized mark-to-market gains/(losses) for economic hedging activities	193			(134		)	(193		)
Reversal of previously recognized unrealized (gains)/losses on settled positions related to trading activity	(25		)	10			(46		)
Reversal of acquired gain positions related to trading activity	—			—			(14		)
Net unrealized gains/(losses) on open positions related to trading activity	14			18			(16		)
Total unrealized mark-to-market (losses)/gains for trading activity	(11		)	28			(76		)
Total unrealized gains/(losses)	$	182		$	(106	)	$	(269	)



	Year Ended December 31,
	2017			2016			2015
	(In millions)
Unrealized gains/(losses) included in operating revenues	$	228		$	(614	)	$	(210	)
Unrealized (losses)/gains included in cost of operations	(46		)	508			(59		)
Total impact to statement of operations — energy commodities	$	182		$	(106	)	$	(269	)
Total impact to statement of operations — interest rate contracts	$	9		$	36		$	17