Accounting for Derivative Instruments and Hedging Activities (Tables)

12 Months Ended

Dec. 31, 2018

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, 2018 and 2017. 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, 2018			December 31, 2017
		(In millions)
Emissions	Short Ton	(2		)	1
Renewables Energy Certificates	Certificates	1			—
Coal	Short Ton	13			21
Natural Gas	MMBtu	(330		)	(20		)
Oil	Barrels	1			—
Power	MWh	1			23
Capacity	MW/Day	(1		)	(1		)
Interest	Dollars	$	1,000		$	1,060
Equity	Shares	—			1

Fair Value Within the Derivative Instrument Valuation On the Balance Sheet

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, 2018		December 31, 2017		December 31, 2018		December 31, 2017
Derivatives Not Designated as Cash Flow or Fair Value Hedges:
Interest rate contracts current	$	17	$	8	$	—	$	1
Interest rate contracts long-term	22		31		—		5
Commodity contracts current	747		616		673		536
Commodity contracts long-term	295		128		304		138
Total Derivatives Not Designated as Cash Flow or Fair Value Hedges	$	1,081	$	783	$	977	$	680

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, 2018	(In millions)
Commodity contracts:
Derivative assets	$	1,042		$	(778	)	$	(31	)	$	233
Derivative liabilities	(977		)	778			114			(85		)
Total commodity contracts	65			—			83			148
Interest rate contracts:
Derivative assets	39			—			—			39
Total interest rate contracts	39			—			—			39
Total derivative instruments	$	104		$	—		$	83		$	187



	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	$	744		$	(578	)	$	(11	)	$	155
Derivative liabilities	(674		)	578			72			(24		)
Total commodity contracts	70			—			61			131
Interest rate contracts:
Derivative assets	39			—			—			39
Derivative liabilities	(6		)	—			—			(6		)
Total interest rate contracts	33			—			—			33
Total derivative instruments	$	103		$	—		$	61		$	164

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

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



	Interest Rate Contracts
	2018			2017			2016
	(In millions)
Accumulated OCI beginning balance	$	(54	)	$	(66	)	$	(101	)
Reclassified from accumulated OCI to income:
Due to realization of previously deferred amounts	8			12			21
Mark-to-market of cash flow hedge accounting contracts	21			—			14
Sale of NRG Yield and Renewables	$	25		$	—		$	—
Accumulated OCI ending balance, net of $0, $8 and $16 tax	$	—		$	(54	)	$	(66	)

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,
	2018			2017			2016
	(In millions)
Unrealized mark-to-market results
Reversal of previously recognized unrealized (gains)/losses on settled positions related to economic hedges	$	(73	)	$	47		$	(128	)
Reversal of acquired gain positions related to economic hedges	(10		)	—			(12		)
Net unrealized gains on open positions related to economic hedges	97			159			12
Total unrealized mark-to-market gains/(losses) for economic hedging activities	14			206			(128		)
Reversal of previously recognized unrealized (gains)/losses on settled positions related to trading activity	(12		)	(25		)	10
Net unrealized gains on open positions related to trading activity	29			14			18
Total unrealized mark-to-market gains/(losses) for trading activity	17			(11		)	28
Total unrealized gains/(losses)	$	31		$	195		$	(100	)



	Year Ended December 31,
	2018			2017			2016
	(In millions)
Unrealized (losses)/gains included in operating revenues	$	(113	)	$	241		$	(608	)
Unrealized gains/(losses) included in cost of operations	144			(46		)	508
Total impact to statement of operations — energy commodities	$	31		$	195		$	(100	)
Total impact to statement of operations — interest rate contracts	$	—		$	4		$	(8	)