Benefit Plans (Fair Value of Plan Assets Measured on a Recurring Basis) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Corporate and other bonds [Member]
Fair value of plan assets	$ 387	$ 315
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	377	305
Corporate and other bonds [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets	10	10
States, municipalities and political subdivisions [Member]
Fair value of plan assets	104	92
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	104	92
States, municipalities and political subdivisions [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets
Residential Mortgage Backed Securities [Member]
Fair value of plan assets	198	179
Residential Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets
Residential Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets	198	179
Residential Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets
Commercial Mortgage Backed Securities [Member]
Fair value of plan assets	68	49
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	68	40
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	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	9
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	276	238
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	276	228
Total asset-backed [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets		10
Fixed Maturities [Member]
Fair value of plan assets	767	645
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	757	625
Fixed Maturities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets	10	20
Equity securities [Member]
Fair value of plan assets	433	504
Equity securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets	353	421
Equity securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets	75	77
Equity securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets	5	6
Short-term Investments [Member]
Fair value of plan assets	98	113
Short-term Investments [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets	63	106
Short-term Investments [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets	35	7
Short-term Investments [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets
Hedge Funds [Member]
Fair value of plan assets	818	912
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	488	518
Hedge Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets	330	394
Private Equity Funds [Member]
Fair value of plan assets	65	59
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	65	59
Total limited partnerships [Member]
Fair value of plan assets	883	971
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	488	518
Total limited partnerships [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets	395	453
Derivative [Member]
Fair value of plan assets		1
Derivative [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets		1
Derivative [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets
Derivative [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets
Other Assets [Member]
Fair value of plan assets	21	15
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	21	15
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	9
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	9
Total assets [Member]
Fair value of plan assets	2,212	2,258
Total assets [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value of plan assets	416	528
Total assets [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value of plan assets	1,376	1,242
Total assets [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value of plan assets	$ 420	$ 488