Fair Value Measurements (Details 2) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
US Treasury and Government [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Purchases and issuances	$ 20
Financial assets, Ending Balance	20
States, municipalities and political subdivisions [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Financial assets, Beginning Balance	83	20	23
Consolidate Managed Investment Entities			0
Total realized/unrealized Gains (losses) included in other comprehensive income (loss)	4	4	1
Purchases and issuances	19	58
Sales and settlements	(7)	(4)
Purchases, sales, issuances and settlements			(4)
Transfer into Level 3	8	17	17
Transfer out of Level 3	(49)	(12)	(17)
Financial assets, Ending Balance	58	83	20
Residential Mortgage Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Financial assets, Beginning Balance	361	312	435
Consolidate Managed Investment Entities			0
Total realized/unrealized gains (losses) included in Net income	5	3	7
Total realized/unrealized Gains (losses) included in other comprehensive income (loss)	17	(9)	26
Purchases and issuances	96	42
Sales and settlements	(45)	(38)
Purchases, sales, issuances and settlements			17
Transfer into Level 3	228	127	27
Transfer out of Level 3	(291)	(76)	(200)
Financial assets, Ending Balance	371	361	312
Commercial Mortgage Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Financial assets, Beginning Balance	19	6	0
Consolidate Managed Investment Entities			0
Total realized/unrealized gains (losses) included in Net income	1	1	0
Total realized/unrealized Gains (losses) included in other comprehensive income (loss)	2
Purchases and issuances		9
Purchases, sales, issuances and settlements			6
Transfer into Level 3		13	0
Transfer out of Level 3		(10)	0
Financial assets, Ending Balance	22	19	6
All other corporate [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Financial assets, Beginning Balance	519	436	311
Consolidate Managed Investment Entities			(6)
Total realized/unrealized gains (losses) included in Net income	10	2	(10)
Total realized/unrealized Gains (losses) included in other comprehensive income (loss)	17	15	10
Purchases and issuances	141	236
Sales and settlements	(71)	(72)
Purchases, sales, issuances and settlements			100
Transfer into Level 3	29	90	118
Transfer out of Level 3	(156)	(188)	(87)
Financial assets, Ending Balance	489	519	436
Trading fixed maturities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Financial assets, Beginning Balance	1	3	1
Consolidate Managed Investment Entities			0
Purchases, sales, issuances and settlements			4
Transfer into Level 3			2
Transfer out of Level 3	(1)	(2)	(4)
Financial assets, Ending Balance	0	1	3
Equity securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Financial assets, Beginning Balance	11	21	25
Consolidate Managed Investment Entities			0
Total realized/unrealized Gains (losses) included in other comprehensive income (loss)	2	1	(1)
Purchases and issuances	30	2
Sales and settlements		(2)
Purchases, sales, issuances and settlements			0
Transfer into Level 3	13	2	0
Transfer out of Level 3	(19)	(13)	(3)
Financial assets, Ending Balance	37	11	21
Assets of Managed Investment Entities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Financial assets, Beginning Balance	44	48	0
Consolidate Managed Investment Entities			90
Total realized/unrealized gains (losses) included in Net income		(8)	8
Purchases and issuances	20	32
Sales and settlements	(14)	(18)
Purchases, sales, issuances and settlements			(16)
Transfer into Level 3	13	9	26
Transfer out of Level 3	(23)	(19)	(60)
Financial assets, Ending Balance	$ 40	$ 44	$ 48