Fair Value (Assets and liabilities measured at fair value on a recurring basis) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Total fixed maturity securities	$ 42,633	$ 39,937
Equity securities	249	304
Other invested assets	59	12
Short term investments	1,832	1,641
Life settlement contracts, included in Other Assets	100	117
Separate account business	312	417
Derivative financial instruments, included in Other liabilities	(3)	(1)
Fair Value, Measurements, Recurring [Member]
Total fixed maturity securities	42,633	39,937
Equity securities	249	304
Other invested assets	59	12
Short term investments	1,792	1,641
Life settlement contracts, included in Other Assets	100	117
Separate account business	312	417
Total assets	45,145	42,428
Derivative financial instruments, included in Other liabilities	(3)	(1)
Total liabilities	(3)	(1)
Fair Value, Measurements, Recurring [Member] | Corporate and other bonds [Member]
Total fixed maturity securities	22,236	20,884
Fair Value, Measurements, Recurring [Member] | States, municipalities and political subdivisions [Member]
Total fixed maturity securities	10,783	9,782
Fair Value, Measurements, Recurring [Member] | Residential mortgage-backed [Member]
Total fixed maturity securities	5,920	5,775
Fair Value, Measurements, Recurring [Member] | Commercial mortgage-backed [Member]
Total fixed maturity securities	1,822	1,354
Fair Value, Measurements, Recurring [Member] | Other asset-backed [Member]
Total fixed maturity securities	952	955
Fair Value, Measurements, Recurring [Member] | Total asset-backed [Member]
Total fixed maturity securities	8,694	8,084
Fair Value, Measurements, Recurring [Member] | U.S. Treasury and obligations of government-sponsored enterprises [Member]
Total fixed maturity securities	182	493
Fair Value, Measurements, Recurring [Member] | Foreign government [Member]
Total fixed maturity securities	613	636
Fair Value, Measurements, Recurring [Member] | Redeemable preferred stock [Member]
Total fixed maturity securities	125	58
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Total fixed maturity securities	344	548
Equity securities	117	124
Other invested assets
Short term investments	987	1,106
Life settlement contracts, included in Other Assets
Separate account business	4	21
Total assets	1,452	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	6
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] | 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] | Total 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	158	451
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Foreign government [Member]
Total fixed maturity securities	140	92
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Redeemable preferred stock [Member]
Total fixed maturity securities	40	5
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Total fixed maturity securities	41,038	37,882
Equity securities	98	113
Other invested assets	58	1
Short term investments	799	508
Life settlement contracts, included in Other Assets
Separate account business	306	373
Total assets	42,299	38,877
Derivative financial instruments, included in Other liabilities	(2)
Total liabilities	(2)
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Corporate and other bonds [Member]
Total fixed maturity securities	22,011	20,402
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | States, municipalities and political subdivisions [Member]
Total fixed maturity securities	10,687	9,611
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Residential mortgage-backed [Member]
Total fixed maturity securities	5,507	5,323
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Commercial mortgage-backed [Member]
Total fixed maturity securities	1,693	1,295
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Other asset-backed [Member]
Total fixed maturity securities	584	612
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Total asset-backed [Member]
Total fixed maturity securities	7,784	7,230
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | U.S. Treasury and obligations of government-sponsored enterprises [Member]
Total fixed maturity securities	24	42
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Foreign government [Member]
Total fixed maturity securities	473	544
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Redeemable preferred stock [Member]
Total fixed maturity securities	59	53
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Total fixed maturity securities	1,251	1,507
Equity securities	34	67
Other invested assets	1	11
Short term investments	6	27
Life settlement contracts, included in Other Assets	100	117
Separate account business	2	23
Total assets	1,394	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	219	482
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | States, municipalities and political subdivisions [Member]
Total fixed maturity securities	96	171
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Residential mortgage-backed [Member]
Total fixed maturity securities	413	452
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Commercial mortgage-backed [Member]
Total fixed maturity securities	129	59
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Other asset-backed [Member]
Total fixed maturity securities	368	343
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Total asset-backed [Member]
Total fixed maturity securities	910	854
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	$ 26