Benefit Plans (Reconciliation of Level 3 Plan Assets) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Corporate and other bonds [Member]
Fair value of plan assets	$ 447	$ 387
Commercial Mortgage Backed Securities [Member]
Fair value of plan assets	105	68
Other asset-backed [Member]
Fair value of plan assets		10
Total asset-backed [Member]
Fair value of plan assets	266	276
Fixed Maturities [Member]
Fair value of plan assets	804	767
Equity securities [Member]
Fair value of plan assets	493	433
Hedge Funds [Member]
Fair value of plan assets	896	818
Private Equity Funds [Member]
Fair value of plan assets	62	65
Total limited partnerships [Member]
Fair value of plan assets	958	883
Investment Contracts with Insurance Company [Member]
Fair value of plan assets	10	10
Total assets [Member]
Fair value of plan assets	2,425	2,212
Fair Value, Inputs, Level 3 [Member] | Corporate and other bonds [Member]
Fair value of plan assets	11	10	10
Defined Benefit Plan, Actual Return on Plan Assets Still Held	1
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period
Defined Benefit Plan, Purchases, Sales, and Settlements
Defined Benefit Plan, Net transfers into (out of) Level 3
Fair Value, Inputs, Level 3 [Member] | Commercial Mortgage Backed Securities [Member]
Fair value of plan assets			9
Defined Benefit Plan, Actual Return on Plan Assets Still Held
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period
Defined Benefit Plan, Purchases, Sales, and Settlements		(9)
Defined Benefit Plan, Net transfers into (out of) Level 3
Fair Value, Inputs, Level 3 [Member] | Other asset-backed [Member]
Fair value of plan assets			1
Defined Benefit Plan, Actual Return on Plan Assets Still Held
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period
Defined Benefit Plan, Purchases, Sales, and Settlements		(1)
Defined Benefit Plan, Net transfers into (out of) Level 3
Fair Value, Inputs, Level 3 [Member] | Total asset-backed [Member]
Fair value of plan assets			10
Defined Benefit Plan, Actual Return on Plan Assets Still Held
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period
Defined Benefit Plan, Purchases, Sales, and Settlements		(10)
Defined Benefit Plan, Net transfers into (out of) Level 3
Fair Value, Inputs, Level 3 [Member] | Fixed Maturities [Member]
Fair value of plan assets	11	10	20
Defined Benefit Plan, Actual Return on Plan Assets Still Held	1
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period
Defined Benefit Plan, Purchases, Sales, and Settlements		(10)
Defined Benefit Plan, Net transfers into (out of) Level 3
Fair Value, Inputs, Level 3 [Member] | Equity securities [Member]
Fair value of plan assets	5	5	6
Defined Benefit Plan, Actual Return on Plan Assets Still Held		(1)
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period
Defined Benefit Plan, Purchases, Sales, and Settlements
Defined Benefit Plan, Net transfers into (out of) Level 3
Fair Value, Inputs, Level 3 [Member] | Hedge Funds [Member]
Fair value of plan assets	359	330	394
Defined Benefit Plan, Actual Return on Plan Assets Still Held	41	5
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period	3	5
Defined Benefit Plan, Purchases, Sales, and Settlements	(15)	(74)
Defined Benefit Plan, Net transfers into (out of) Level 3
Fair Value, Inputs, Level 3 [Member] | Private Equity Funds [Member]
Fair value of plan assets	62	65	59
Defined Benefit Plan, Actual Return on Plan Assets Still Held	8	9
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period
Defined Benefit Plan, Purchases, Sales, and Settlements	(11)	(3)
Defined Benefit Plan, Net transfers into (out of) Level 3
Fair Value, Inputs, Level 3 [Member] | Total limited partnerships [Member]
Fair value of plan assets	421	395	453
Defined Benefit Plan, Actual Return on Plan Assets Still Held	49	14
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period	3	5
Defined Benefit Plan, Purchases, Sales, and Settlements	(26)	(77)
Defined Benefit Plan, Net transfers into (out of) Level 3
Fair Value, Inputs, Level 3 [Member] | Investment Contracts with Insurance Company [Member]
Fair value of plan assets	10	10	9
Defined Benefit Plan, Actual Return on Plan Assets Still Held		1
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period
Defined Benefit Plan, Purchases, Sales, and Settlements
Defined Benefit Plan, Net transfers into (out of) Level 3
Fair Value, Inputs, Level 3 [Member] | Total assets [Member]
Fair value of plan assets	447	420	488
Defined Benefit Plan, Actual Return on Plan Assets Still Held	50	14
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period	3	5
Defined Benefit Plan, Purchases, Sales, and Settlements	(26)	(87)
Defined Benefit Plan, Net transfers into (out of) Level 3