Retirement Benefits (Tables)

12 Months Ended

Dec. 31, 2011

Defined Benefit Plan Disclosure [Line Items]

Weighted average rates assumed in actuarial calculations used to determine both benefit obligations as of measurement date and net periodic costs for pension and other postretirement benefit plans

	2011			2010			2009
Discount rate:
Pension plans		4.98	%		5.52	%	5.93%
Other postretirement benefit plans		4.88			5.40		5.83
Annual salary increase		3.84			3.84		4.18
Long-term return on plan assets:
Pension plans*		8.45			8.45		8.20
Other postretirement benefit plans		7.39			7.40		7.51

Effect of 1% annual increase or decrease in assumed medical care cost on APBO and service and interest cost components

	1 Percent Increase		1 Percent   Decrease
	(in millions)
Benefit obligation		$125		$(106)
Service and interest costs		7		(6)

Changes projected benefit obligations and fair value of plan assets

		$(1,279)			$(1,279)
	2011			2010
	(in millions)
Change in benefit obligation
Benefit obligation at beginning of year	$	7,223		$	6,758
Service cost		184			172
Interest cost		389			391
Benefits paid		(324	)		(296)
Actuarial loss (gain)		607			198
Balance at end of year		8,079			7,223
Change in plan assets
Fair value of plan assets at beginning of year		6,834			5,627
Actual return (loss) on plan assets		256			859
Employer contributions		34			644
Benefits paid		(324	)		(296)
Fair value of plan assets at end of year		6,800			6,834
Accrued liability	$	(1,279	)	$	(389)

Amounts related to defined benefit pension plans that had not yet been recognized in net periodic pension cost along with estimated amortization

	Prior Service Cost		Net (Gain) Loss
	(in millions)
Balance at December 31, 2011:
Accumulated OCI		$    7		$   102
Regulatory assets		128		2,486
Total		$135		$2,588
Balance at December 31, 2010:
Accumulated OCI		$    8		$     60
Regulatory assets		159		1,590
Total		$167		$1,650
Estimated amortization in net periodic pension cost in 2012:
Accumulated OCI		$    1		$       4
Regulatory assets		29		91
Total		$  30		$     95

Components of other comprehensive income along with changes in balances of regulatory assets and regulatory liabilities related to defined benefit pension plans

	Accumulated OCI		Regulatory         Assets
	(in millions)
Balance at December 31, 2009		$  74		$1,894
Net (gain) loss		(4)		(106)
Change in prior service costs		—		2
Reclassification adjustments:
Amortization of prior service costs		(1)		(32)
Amortization of net gain (loss)		(1)		(9)
Total reclassification adjustments		(2)		(41)
Total change		(6)		(145)
Balance at December 31, 2010		$  68		$1,749
Net (gain) loss		43		915
Change in prior service costs		—		1
Reclassification adjustments:
Amortization of prior service costs		(1)		(31)
Amortization of net gain (loss)		(1)		(20)
Total reclassification adjustments		(2)		(51)
Total change		41		865
Balance at December 31, 2011		$109		$2,614

Estimated pension benefit payments

	Benefit Payments
	(in millions)
2012		$    361
2013		380
2014		398
2015		418
2016		438
2017 to 2021		2,488

Changes in the accumulated postretirement benefit obligations (APBO) and in fair value of plan assets

	2011		2010
	(in millions)
Change in benefit obligation
Benefit obligation at beginning of year	$	1,752	$	1,759
Service cost		21		25
Interest cost		92		100
Benefits paid		(103)		(95)
Actuarial loss (gain)		29		(41)
Plan amendments		(12)		(2)
Retiree drug subsidy		8		6
Balance at end of year		1,787		1,752
Change in plan assets
Fair value of plan assets at beginning of year		802		743
Actual return (loss) on plan assets		4		82
Employer contributions		54		66
Benefits paid		(95)		(89)
Fair value of plan assets at end of year		765		802
Accrued liability	$	(1,022)	$	(950)

Amounts included in accumulated other comprehensive income and regulatory assets related to other postretirement benefit plans

	Prior Service Cost		Net (Gain) Loss		Transition Obligation
			(in millions)
Balance at December 31, 2011:
Accumulated OCI		$—		$    6		$—
Regulatory assets		17		314		14
Total		$17		$320		$14
Balance at December 31, 2010:
Accumulated OCI		$—		$    3		$—
Regulatory assets		34		233		25
Total		$34		$236		$25
Estimated amortization as net periodic postretirement benefit cost in 2012:
Accumulated OCI		$—		$  —		$—
Regulatory assets		4		6		10
Total		$  4		$    6		$10

Components of other comprehensive income along with changes in balance of regulatory assets related to other postretirement benefit plans

	Accumulated OCI		Regulatory         Assets
	(in millions)
Balance at December 31, 2009		$  5		$  374
Net (gain) loss		(2)		(60)
Change in prior service costs/transition obligation		—		(2)
Reclassification adjustments:
Amortization of transition obligation		—		(10)
Amortization of prior service costs		—		(5)
Amortization of net gain (loss)		—		(5)
Total reclassification adjustments		—		(20)
Total change		(2)		(82)
Balance at December 31, 2010		$  3		$  292
Net (gain) loss		3		84
Change in prior service costs/transition obligation		—		(12)
Reclassification adjustments:
Amortization of transition obligation		—		(10)
Amortization of prior service costs		—		(5)
Amortization of net gain (loss)		—		(4)
Total reclassification adjustments		—		(19)
Total change		3		53
Balance at December 31, 2011		$  6		$  345

Summary of estimation of future benefit payments and subsidy receipts based on assumptions used to measure accumulated benefit obligation for postretirement plans

	Benefit Payments	Subsidy Receipts	Total
	(in millions)
2012	$110	$(10)	$100
2013	116	(12)	104
2014	122	(13)	109
2015	128	(15)	113
2016	133	(16)	117
2017 to 2021	691	(90)	601

Composition of pension plan assets along with targeted mix of assets

	Target	2011			2010
Pension plan assets:
Domestic equity	26%		29	%	29%
International equity	25		25		27
Fixed income	23		23		22
Special situations	3		—		—
Real estate investments	14		14		13
Private equity	9		9		9
Total	100%		100	%	100%
Other postretirement benefit plan assets:
Domestic equity	41%		39	%	40%
International equity	17		18		21
Domestic fixed income	30		31		29
Global fixed income	3		4		3
Special situations	1		—		—
Real estate investments	5		5		4
Private equity	3		3		3
Total	100%		100	%	100%

Pension Plans [Member]

Defined Benefit Plan Disclosure [Line Items]

Amounts recognized in consolidated balance sheets related to company's benefit plans

		$(1,279)			$(1,279)
	2011			2010
	(in millions)
Prepaid pension costs	$	—		$	88
Other regulatory assets, deferred		2,614			1,749
Other current liabilities		(34	)		(28)
Employee benefit obligations		(1,245	)		(449)
Accumulated OCI		109			68

Components of net periodic benefit cost

	2011			2010			2009
	(in millions)
Service cost	$	184		$	172		$	146
Interest cost		389			391			387
Expected return on plan assets		(607	)		(552	)		(541)
Recognized net loss		21			10			7
Net amortization		32			33			35
Net periodic pension cost	$	19		$	54		$	34

Fair values of benefit plan assets

	Fair Value Measurements Using
	Quoted Prices   in Active Markets for Identical Assets		Significant Other Observable Inputs		Significant   Unobservable   Inputs
As of December 31, 2011:	(Level 1)		(Level 2)		(Level 3)		Total
	(in millions)
Assets:
Domestic equity*		$1,155		$   533		$    —		$1,688
International equity*		1,187		340		—		1,527
Fixed income:
U.S. Treasury, government, and agency bonds		—		433		—		433
Mortgage- and asset-backed securities		—		135		—		135
Corporate bonds		—		832		3		835
Pooled funds		—		380		—		380
Cash equivalents and other		1		139		—		140
Real estate investments		220		—		782		1,002
Private equity		—		—		582		582
Total		$2,563		$2,792		$1,367		$6,722

* Level 1 securities consist of actively traded stocks while Level 2 securities consist of pooled funds. Management believes that the portfolio is well-diversified with no significant concentrations of risk.

	Fair Value Measurements Using
	Quoted Prices   in Active Markets for Identical Assets		Significant Other Observable Inputs		Significant   Unobservable   Inputs
As of December 31, 2010:	(Level 1)		(Level 2)		(Level 3)		Total
	(in millions)
Assets:
Domestic equity*		$1,266		$   511		$       1		$1,778
International equity*		1,277		443		—		1,720
Fixed income:
U.S. Treasury, government, and agency bonds		—		304		—		304
Mortgage- and asset-backed securities		—		247		—		247
Corporate bonds		—		594		2		596
Pooled funds		—		201		—		201
Cash equivalents and other		2		478		—		480
Real estate investments		184		—		674		858
Private equity		—		—		638		638
Total		$2,729		$2,778		$1,315		$6,822
Liabilities:
Derivatives		(1)		—		—		(1)
Total		$2,728		$2,778		$1,315		$6,821

* Level 1 securities consist of actively traded stocks while Level 2 securities consist of pooled funds. Management believes that the portfolio is well-diversified with no significant concentrations of risk.

Changes in fair value measurement of the level 3 items in benefit plan assets

	2011		2010
	Real Estate   Investments	Private Equity	Real Estate     Investments	Private Equity
	(in millions)
Beginning balance	$674	$638	$547	$555
Actual return on investments:
Related to investments held at year end	72	(12)	59	67
Related to investments sold during the year	20	47	18	18
Total return on investments	92	35	77	85
Purchases, sales, and settlements	16	(91)	50	(2)
Transfers into/out of Level 3	—	—	—	—
Ending balance	$782	$582	$674	$638

Other Postretirement Benefits [Member]

Defined Benefit Plan Disclosure [Line Items]

Weighted average medical care cost trend rates used in measuring the APBO

	Initial Cost     Trend Rate	Ultimate            Cost Trend            Rate	Year That   Ultimate   Rate Is   Reached
Pre-65	8.00%	5.00%	2019
Post-65 medical	6.00	5.00	2019
Post-65 prescription	6.00	5.00	2023

Amounts recognized in consolidated balance sheets related to company's benefit plans

	2011		2010
	(in millions)
Other regulatory assets, deferred	$	345	$	292
Other current liabilities		(4)		(1)
Employee benefit obligations		(1,018)		(949)
Accumulated OCI		6		3

Components of net periodic benefit cost

	2011		2010		2009
	(in millions)
Service cost		$  21		$  25		$  26
Interest cost		92		100		113
Expected return on plan assets		(64)		(63)		(61)
Net amortization		20		20		25
Net postretirement cost		$  69		$  82		$103

Fair values of benefit plan assets

	Fair Value Measurements Using
As of December 31, 2011:	Quoted Prices   in Active Markets for Identical Assets (Level 1)	Significant Other Observable Inputs (Level 2)	Significant   Unobservable   Inputs (Level 3)	Total
	(in millions)
Assets:
Domestic equity*	$156	$  38	$—	$194
International equity*	45	39	—	84
Fixed income:
U.S. Treasury, government, and agency bonds	—	24	—	24
Mortgage- and asset-backed securities	—	5	—	5
Corporate bonds	—	32	—	32
Pooled funds	—	48	—	48
Cash equivalents and other	—	46	—	46
Trust-owned life insurance	—	291	—	291
Real estate investments	9	—	30	39
Private equity	—	—	23	23
Total	$210	$523	$53	$786

* Level 1 securities consist of actively traded stocks while Level 2 securities consist of pooled funds. Management believes that the portfolio is well-diversified with no significant concentrations of risk.

	Fair Value Measurements Using
	Quoted Prices   in Active Markets for Identical Assets	Significant Other Observable Inputs	Significant   Unobservable   Inputs
As of December 31, 2010:	(Level 1)	(Level 2)	(Level 3)	Total
	(in millions)
Assets:
Domestic equity*	$176	$  45	$—	$221
International equity*	49	50	—	99
Fixed income:
U.S. Treasury, government, and agency bonds	—	15	—	15
Mortgage- and asset-backed securities	—	10	—	10
Corporate bonds	—	23	—	23
Pooled funds	—	34	—	34
Cash equivalents and other	—	41	—	41
Trust-owned life insurance	—	291	—	291
Real estate investments	7	—	26	33
Private equity	—	—	23	23
Total	$232	$509	$49	$790

* Level 1 securities consist of actively traded stocks while Level 2 securities consist of pooled funds. Management believes that the portfolio is well-diversified with no significant concentrations of risk.

Changes in fair value measurement of the level 3 items in benefit plan assets

	2011		2010
	Real Estate   Investments	Private Equity	Real Estate     Investments	Private Equity
	(in millions)
Beginning balance	$26	$23	$24	$24
Actual return on investments:
Related to investments held at year end	3	—	2	1
Related to investments sold during the year	1	2	—	—
Total return on investments	4	2	2	1
Purchases, sales, and settlements	—	(2)	—	(2)
Transfers into/out of Level 3	—	—	—	—
Ending balance	$30	$23	$26	$23