Benefit Plans (Fair Value of Plan Assets Measured on a Recurring Basis) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Corporate and other bonds [Member]
Fair value of plan assets	$ 447	$ 387
Corporate and other bonds [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets
Corporate and other bonds [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets	436	377
Corporate and other bonds [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets	11	10	10
States, municipalities and political subdivisions [Member]
Fair value of plan assets	91	104
States, municipalities and political subdivisions [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets
States, municipalities and political subdivisions [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets	91	104
States, municipalities and political subdivisions [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets
Residential mortgage-backed [Member]
Fair value of plan assets	161	198
Residential mortgage-backed [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets
Residential mortgage-backed [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets	161	198
Residential mortgage-backed [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets
Commercial Mortgage Backed Securities [Member]
Fair value of plan assets	105	68
Commercial Mortgage Backed Securities [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets
Commercial Mortgage Backed Securities [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets	105	68
Commercial Mortgage Backed Securities [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets			9
Other asset-backed [Member]
Fair value of plan assets		10
Other asset-backed [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets
Other asset-backed [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets		10
Other asset-backed [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets			1
Total asset-backed [Member]
Fair value of plan assets	266	276
Total asset-backed [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets
Total asset-backed [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets	266	276
Total asset-backed [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets			10
Fixed Maturities [Member]
Fair value of plan assets	804	767
Fixed Maturities [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets
Fixed Maturities [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets	793	757
Fixed Maturities [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets	11	10	20
Equity securities [Member]
Fair value of plan assets	493	433
Equity securities [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets	386	353
Equity securities [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets	102	75
Equity securities [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets	5	5	6
Derivative Financial Instruments, Assets [Member]
Fair value of plan assets	1
Derivative Financial Instruments, Assets [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets	1
Derivative Financial Instruments, Assets [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets
Derivative Financial Instruments, Assets [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets
Short-term Investments [Member]
Fair value of plan assets	119	98
Short-term Investments [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets	37	63
Short-term Investments [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets	82	35
Short-term Investments [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets
Hedge Funds [Member]
Fair value of plan assets	896	818
Hedge Funds [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets
Hedge Funds [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets	537	488
Hedge Funds [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets	359	330	394
Private Equity Funds [Member]
Fair value of plan assets	62	65
Private Equity Funds [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets
Private Equity Funds [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets
Private Equity Funds [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets	62	65	59
Total limited partnerships [Member]
Fair value of plan assets	958	883
Total limited partnerships [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets
Total limited partnerships [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets	537	488
Total limited partnerships [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets	421	395	453
Other Assets [Member]
Fair value of plan assets	40	21
Other Assets [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets
Other Assets [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets	40	21
Other Assets [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets
Investment Contracts with Insurance Company [Member]
Fair value of plan assets	10	10
Investment Contracts with Insurance Company [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets
Investment Contracts with Insurance Company [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets
Investment Contracts with Insurance Company [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets	10	10	9
Total assets [Member]
Fair value of plan assets	2,425	2,212
Total assets [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets	424	416
Total assets [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets	1,554	1,376
Total assets [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets	$ 447	$ 420	$ 488

Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. If a plan has liabilities other than for benefits, those non-benefit obligations may be considered as reductions of plan assets.

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