Fair Value Measurements (Details 2) (USD $) In Millions, unless otherwise specified	9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended							3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2012 US Treasury and Government [Member]	Jun. 30, 2012 US Treasury and Government [Member]	Sep. 30, 2012 States, municipalities and political subdivisions [Member]	Sep. 30, 2011 States, municipalities and political subdivisions [Member]	Sep. 30, 2012 States, municipalities and political subdivisions [Member]	Sep. 30, 2011 States, municipalities and political subdivisions [Member]	Sep. 30, 2012 Residential Mortgage Backed Securities [Member]	Sep. 30, 2011 Residential Mortgage Backed Securities [Member]	Sep. 30, 2012 Residential Mortgage Backed Securities [Member]	Sep. 30, 2011 Residential Mortgage Backed Securities [Member]	Sep. 30, 2012 Commercial Mortgage Backed Securities [Member]	Sep. 30, 2011 Commercial Mortgage Backed Securities [Member]	Sep. 30, 2012 Commercial Mortgage Backed Securities [Member]	Sep. 30, 2011 Commercial Mortgage Backed Securities [Member]	Sep. 30, 2012 All other corporate [Member]	Sep. 30, 2011 All other corporate [Member]	Sep. 30, 2012 All other corporate [Member]	Sep. 30, 2011 All other corporate [Member]	Sep. 30, 2011 Trading fixed maturities [Member]	Sep. 30, 2012 Trading fixed maturities [Member]	Jun. 30, 2012 Trading fixed maturities [Member]	Dec. 31, 2011 Trading fixed maturities [Member]	Jun. 30, 2011 Trading fixed maturities [Member]	Sep. 30, 2012 Equity securities [Member]	Sep. 30, 2011 Equity securities [Member]	Sep. 30, 2012 Equity securities [Member]	Sep. 30, 2011 Equity securities [Member]	Sep. 30, 2012 Assets of Managed Investment Entities [Member]	Sep. 30, 2011 Assets of Managed Investment Entities [Member]	Sep. 30, 2012 Assets of Managed Investment Entities [Member]	Sep. 30, 2011 Assets of Managed Investment Entities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Financial assets, Beginning Balance		$ 20	$ 86	$ 84	$ 83	$ 20	$ 320	$ 255	$ 361	$ 312	$ 20	$ 10	$ 19	$ 6	$ 537	$ 382	$ 519	$ 436	$ 3	$ 1	$ 1	$ 1	$ 1	$ 41	$ 21	$ 11	$ 21	$ 54	$ 53	$ 44	$ 48
Total realized/unrealized gains (losses) included in Net income							3	1	5	2	1		1		2	2	9	1											(6)		(7)
Total realized/unrealized Gains (losses) included in other comprehensive income (loss)			2	4	4	5	7	(5)	11	(8)			1		6	12	18	17							(1)		1
Purchases and issuances	20		0	0	19	53	15	25	86	42		9		9	67	32	124	123						4	2	30	2	0	5	13	21
Sales and Settlements			(6)	(3)	(7)	(3)	(11)	(9)	(29)	(29)					(19)	(14)	(57)	(51)									(2)	(1)	(7)	(13)	(13)
Transfer into Level 3			4	0	9	10	86	24	167	31		9		13	1	46	29	70						9	2	13	2		0	14	8
Transfer out of Level 3			(28)	(13)	(50)	(13)	(53)	(7)	(234)	(66)	0				(99)	(24)	(147)	(160)	(2)					(18)		(18)		(18)	(5)	(23)	(17)
Financial assets, Ending Balance	$ 20	$ 20	$ 58	$ 72	$ 58	$ 72	$ 367	$ 284	$ 367	$ 284	$ 21	$ 28	$ 21	$ 28	$ 495	$ 436	$ 495	$ 436	$ 1	$ 1	$ 1	$ 1	$ 1	$ 36	$ 24	$ 36	$ 24	$ 35	$ 40	$ 35	$ 40