Fair Value (Assets and liabilities measured at fair value on a recurring basis) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Total fixed maturity securities	$ 42,305	$ 39,937
Equity securities	260	304
Short term investments	2,484	1,641
Separate account business	345	417
Fair Value, Measurements, Recurring [Member]
Total fixed maturity securities	42,305	39,937
Equity securities	260	304
Derivative and other financial instruments, included in Other invested assets	11	12
Short term investments	2,440	1,641
Life settlement contracts, included in Other assets	113	117
Separate account business	345	417
Total assets	45,474	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	21,828	20,884
Fair Value, Measurements, Recurring [Member] | States, municipalities and political subdivisions [Member]
Total fixed maturity securities	10,812	9,782
Fair Value, Measurements, Recurring [Member] | Total asset-backed [Member]
Total fixed maturity securities	8,744	8,084
Fair Value, Measurements, Recurring [Member] | Residential mortgage-backed [Member]
Total fixed maturity securities	6,090	5,775
Fair Value, Measurements, Recurring [Member] | Commercial mortgage-backed [Member]
Total fixed maturity securities	1,688	1,354
Fair Value, Measurements, Recurring [Member] | Other asset-backed [Member]
Total fixed maturity securities	966	955
Fair Value, Measurements, Recurring [Member] | U.S. Treasury and obligations of government-sponsored enterprises [Member]
Total fixed maturity securities	192	493
Fair Value, Measurements, Recurring [Member] | Foreign government [Member]
Total fixed maturity securities	614	636
Fair Value, Measurements, Recurring [Member] | Redeemable preferred stock [Member]
Total fixed maturity securities	115	58
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Total fixed maturity securities	336	548
Equity securities	98	124
Derivative and other financial instruments, included in Other invested assets
Short term investments	1,209	1,106
Life settlement contracts, included in Other assets
Separate account business	4	21
Total assets	1,647	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	168	451
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Foreign government [Member]
Total fixed maturity securities	139	92
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Redeemable preferred stock [Member]
Total fixed maturity securities	29	5
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Total fixed maturity securities	40,670	37,882
Equity securities	112	113
Derivative and other financial instruments, included in Other invested assets		1
Short term investments	1,223	508
Life settlement contracts, included in Other assets
Separate account business	338	373
Total assets	42,343	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	21,569	20,402
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | States, municipalities and political subdivisions [Member]
Total fixed maturity securities	10,723	9,611
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Total asset-backed [Member]
Total fixed maturity securities	7,819	7,230
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Residential mortgage-backed [Member]
Total fixed maturity securities	5,653	5,323
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Commercial mortgage-backed [Member]
Total fixed maturity securities	1,571	1,295
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Other asset-backed [Member]
Total fixed maturity securities	595	612
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	475	544
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Redeemable preferred stock [Member]
Total fixed maturity securities	60	53
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Total fixed maturity securities	1,299	1,507
Equity securities	50	67
Derivative and other financial instruments, included in Other invested assets	11	11
Short term investments	8	27
Life settlement contracts, included in Other assets	113	117
Separate account business	3	23
Total assets	1,484	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	259	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	925	854
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Residential mortgage-backed [Member]
Total fixed maturity securities	437	452
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Commercial mortgage-backed [Member]
Total fixed maturity securities	117	59
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Other asset-backed [Member]
Total fixed maturity securities	371	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	$ 26