Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2015

Fair Value Disclosures [Abstract]

Fair value of assets and liabilities that are measured at fair value on a recurring basis

The following table presents the fair value at March 31, 2015, of our assets and liabilities that are measured at fair value on a recurring basis (dollars in millions):

	Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)			Significant Unobservable Inputs (a) (Level 3)			Other				Balance at March 31, 2015
Assets
Risk management activities — derivative instruments:
Commodity contracts	$	—	$	16		$	33		$	(17	)	(b)	$	32
Nuclear decommissioning trust:
U.S. commingled equity funds	—		313			—			—				313
Fixed income securities:
U.S. Treasury	103		—			—			—				103
Cash and cash equivalent funds	—		10			—			(2		)	(c)	8
Corporate debt	—		115			—			—				115
Mortgage-backed securities	—		88			—			—				88
Municipality bonds	—		85			—			—				85
Other	—		15			—			—				15
Subtotal nuclear decommissioning trust	103		626			—			(2		)		727
Total	$	103	$	642		$	33		$	(19	)		$	759
Liabilities
Risk management activities — derivative instruments:
Commodity contracts	$	—	$	(122	)	$	(82	)	$	68		(b)	$	(136	)

(a) Primarily consists of heat rate options and other long-dated electricity contracts.

(b) Represents counterparty netting, margin and collateral (see Note 7).

(c) Represents nuclear decommissioning trust net pending securities sales and purchases.

The following table presents the fair value at December 31, 2014, of our assets and liabilities that are measured at fair value on a recurring basis (dollars in millions):

	Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)			Significant Unobservable Inputs (a) (Level 3)			Other				Balance at December 31, 2014
Assets
Risk management activities — derivative instruments:
Commodity contracts	$	—	$	21		$	33		$	(23	)	(b)	$	31
Nuclear decommissioning trust:
U.S. commingled equity funds	—		310			—			—				310
Fixed income securities:
U.S. Treasury	119		—			—			—				119
Cash and cash equivalent funds	—		11			—			(7		)	(c)	4
Corporate debt	—		109			—			—				109
Mortgage-backed securities	—		89			—			—				89
Municipality bonds	—		69			—			—				69
Other	—		14			—			—				14
Subtotal nuclear decommissioning trust	119		602			—			(7		)		714
Total	$	119	$	623		$	33		$	(30	)		$	745
Liabilities
Risk management activities — derivative instruments:
Commodity contracts	$	—	$	(95	)	$	(74	)	$	59		(b)	$	(110	)

(a) Primarily consists of heat rate options and other long-dated electricity contracts.

(b) Represents counterparty netting, margin and collateral (see Note 7).

(c) Represents nuclear decommissioning trust net pending securities sales and purchases.

Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments

The following tables provide information regarding our significant unobservable inputs used to value our risk management derivative Level 3 instruments at March 31, 2015 and December 31, 2014:

	March 31, 2015 Fair Value (millions)				Valuation Technique	Significant Unobservable Input		Weighted-Average
Commodity Contracts	Assets		Liabilities				Range
Electricity:
Forward Contracts (a)	$	31	$	60	Discounted cash flows	Electricity forward price (per MWh)	$18.88 - $46.54	$	30.49
Option Contracts (b)	—		15		Option model	Electricity forward price (per MWh)	$30.24 - $60.45	$	41.81
						Natural gas forward price (per MMBtu)	$2.35 - $2.88	$	2.83
						Electricity price volatilities	27% - 86%	54		%
						Natural gas price volatilities	26% - 43%	32		%
Natural Gas:
Forward Contracts (a)	2		7		Discounted cash flows	Natural gas forward price (per MMBtu)	$2.30 - $3.59	$	3.01
Total	$	33	$	82

(a) Includes swaps and physical and financial contracts.

(b) Electricity and natural gas price volatilities are estimated based on historical forward price movements due to lack of market quotes for implied volatilities.

	December 31, 2014 Fair Value (millions)				Valuation Technique	Significant Unobservable Input		Weighted-Average
Commodity Contracts	Assets		Liabilities				Range
Electricity:
Forward Contracts (a)	$	30	$	56	Discounted cash flows	Electricity forward price (per MWh)	$19.51 - $56.72	$	35.27
Option Contracts (b)	—		15		Option model	Electricity forward price (per MWh)	$32.14 - $66.09	$	45.83
						Natural gas forward price (per MMBtu)	$3.18 - $3.29	$	3.25
						Electricity price volatilities	23% - 63%	41		%
						Natural gas price volatilities	23% - 41%	31		%
Natural Gas:
Forward Contracts (a)	3		3		Discounted cash flows	Natural gas forward price (per MMBtu)	$2.98 - $4.13	$	3.45
Total	$	33	$	74

(a) Includes swaps and physical and financial contracts.

(b) Electricity and natural gas price volatilities are estimated based on historical forward price movements due to lack of market quotes for implied volatilities.

Changes in fair value for assets and liabilities that are measured at fair value on a recurring basis using Level 3 inputs

The following table shows the changes in fair value for our risk management activities' assets and liabilities that are measured at fair value on a recurring basis using Level 3 inputs for the three months ended March 31, 2015 and 2014 (dollars in millions):

	Three Months Ended   March 31,
Commodity Contracts	2015			2014
Net derivative balance at beginning of period	$	(41	)	$	(49	)
Total net gains (losses) realized/unrealized:
Deferred as a regulatory asset or liability	(11		)	4
Settlements	—			—
Transfers into Level 3 from Level 2	(1		)	(3		)
Transfers from Level 3 into Level 2	4			(1		)
Net derivative balance at end of period	$	(49	)	$	(49	)
Net unrealized gains included in earnings related to instruments still held at end of period	$	—		$	—