Fair Value (Assets and liabilities measured at fair value on a recurring basis) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Total fixed maturity securities	$ 41,367	$ 39,937
Equity securities	290	304
Short term investments	1,752	1,641
Separate account business	370	417
Derivative financial instruments, included in Other liabilities	(1)	(1)
Fair Value, Measurements, Recurring [Member]
Total fixed maturity securities	41,367	39,937
Equity securities	290	304
Derivative and other financial instruments, included in Other invested assets	11	12
Short term investments	1,500	1,641
Life settlement contracts, included in Other assets	116	117
Separate account business	370	417
Total assets	43,654	42,428
Derivative financial instruments, included in Other liabilities	(1)	(1)
Total liabilities	(1)	(1)
Fair Value, Measurements, Recurring [Member] | Corporate and other bonds [Member]
Total fixed maturity securities	21,492	20,884
Fair Value, Measurements, Recurring [Member] | States, municipalities and political subdivisions [Member]
Total fixed maturity securities	10,416	9,782
Fair Value, Measurements, Recurring [Member] | Total asset-backed [Member]
Total fixed maturity securities	8,525	8,084
Fair Value, Measurements, Recurring [Member] | Residential mortgage-backed [Member]
Total fixed maturity securities	5,891	5,775
Fair Value, Measurements, Recurring [Member] | Commercial mortgage-backed [Member]
Total fixed maturity securities	1,569	1,354
Fair Value, Measurements, Recurring [Member] | Other asset-backed [Member]
Total fixed maturity securities	1,065	955
Fair Value, Measurements, Recurring [Member] | U.S. Treasury and obligations of government-sponsored enterprises [Member]
Total fixed maturity securities	184	493
Fair Value, Measurements, Recurring [Member] | Foreign government [Member]
Total fixed maturity securities	639	636
Fair Value, Measurements, Recurring [Member] | Redeemable preferred stock [Member]
Total fixed maturity securities	111	58
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Total fixed maturity securities	290	548
Equity securities	106	124
Derivative and other financial instruments, included in Other invested assets
Short term investments	1,225	1,106
Life settlement contracts, included in Other assets
Separate account business	12	21
Total assets	1,633	1,799
Derivative financial instruments, included in Other liabilities
Total liabilities
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Corporate and other bonds [Member]
Total fixed maturity securities
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | States, municipalities and political subdivisions [Member]
Total fixed maturity securities
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Total asset-backed [Member]
Total fixed maturity securities
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Residential mortgage-backed [Member]
Total fixed maturity securities
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Commercial mortgage-backed [Member]
Total fixed maturity securities
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Other asset-backed [Member]
Total fixed maturity securities
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | U.S. Treasury and obligations of government-sponsored enterprises [Member]
Total fixed maturity securities	142	451
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Foreign government [Member]
Total fixed maturity securities	120	92
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Redeemable preferred stock [Member]
Total fixed maturity securities	28	5
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Total fixed maturity securities	39,430	37,882
Equity securities	91	113
Derivative and other financial instruments, included in Other invested assets		1
Short term investments	271	508
Life settlement contracts, included in Other assets
Separate account business	355	373
Total assets	40,147	38,877
Derivative financial instruments, included in Other liabilities
Total liabilities
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Corporate and other bonds [Member]
Total fixed maturity securities	21,004	20,402
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | States, municipalities and political subdivisions [Member]
Total fixed maturity securities	10,327	9,611
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Total asset-backed [Member]
Total fixed maturity securities	7,482	7,230
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Residential mortgage-backed [Member]
Total fixed maturity securities	5,448	5,323
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Commercial mortgage-backed [Member]
Total fixed maturity securities	1,403	1,295
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Other asset-backed [Member]
Total fixed maturity securities	631	612
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | U.S. Treasury and obligations of government-sponsored enterprises [Member]
Total fixed maturity securities	42	42
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Foreign government [Member]
Total fixed maturity securities	519	544
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Redeemable preferred stock [Member]
Total fixed maturity securities	56	53
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Total fixed maturity securities	1,647	1,507
Equity securities	93	67
Derivative and other financial instruments, included in Other invested assets	11	11
Short term investments	4	27
Life settlement contracts, included in Other assets	116	117
Separate account business	3	23
Total assets	1,874	1,752
Derivative financial instruments, included in Other liabilities	(1)	(1)
Total liabilities	(1)	(1)
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Corporate and other bonds [Member]
Total fixed maturity securities	488	482
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | States, municipalities and political subdivisions [Member]
Total fixed maturity securities	89	171
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Total asset-backed [Member]
Total fixed maturity securities	1,043	854
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Residential mortgage-backed [Member]
Total fixed maturity securities	443	452
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Commercial mortgage-backed [Member]
Total fixed maturity securities	166	59
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Other asset-backed [Member]
Total fixed maturity securities	434	343
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | U.S. Treasury and obligations of government-sponsored enterprises [Member]
Total fixed maturity securities
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Foreign government [Member]
Total fixed maturity securities
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Redeemable preferred stock [Member]
Total fixed maturity securities	$ 27