Fair Value Measurements (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
US Treasury and Government [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Financial assets, Beginning Balance	$ 20
Purchases and issuances
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	58	83
Total realized/unrealized gains (losses) included in other comprehensive income (loss)
Purchases and issuances		10
Sales and Settlements
Transfer into Level 3
Transfer out of Level 3	(4)	(21)
Financial assets, Ending Balance	54	72
Residential Mortgage Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Financial assets, Beginning Balance	371	361
Total realized/unrealized gains (losses) included in Net income	2	1
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	6
Purchases and issuances	6	8
Sales and Settlements	(12)	(10)
Transfer into Level 3	16	60
Transfer out of Level 3	(35)	(106)
Financial assets, Ending Balance	354	314
Commercial Mortgage Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Financial assets, Beginning Balance	22	19
Total realized/unrealized gains (losses) included in Net income	1
Total realized/unrealized gains (losses) included in other comprehensive income (loss)		1
Purchases and issuances
Transfer into Level 3	7
Financial assets, Ending Balance	30	20
Asset-backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Financial assets, Beginning Balance	253	220
Total realized/unrealized gains (losses) included in Net income	1	1
Total realized/unrealized gains (losses) included in other comprehensive income (loss)		5
Purchases and issuances	12	8
Sales and Settlements	(6)	(5)
Transfer into Level 3		10
Transfer out of Level 3	(15)
Financial assets, Ending Balance	245	239
All other corporate [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Financial assets, Beginning Balance	236	299
Total realized/unrealized gains (losses) included in Net income		1
Total realized/unrealized gains (losses) included in other comprehensive income (loss)		(2)
Purchases and issuances	10	18
Sales and Settlements	(2)	(11)
Transfer into Level 3		11
Transfer out of Level 3		(40)
Financial assets, Ending Balance	244	276
Trading fixed maturities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Financial assets, Beginning Balance		1
Transfer out of Level 3
Financial assets, Ending Balance		1
Equity securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Financial assets, Beginning Balance	37	11
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	3
Purchases and issuances	9	9
Sales and Settlements
Transfer into Level 3		4
Transfer out of Level 3
Financial assets, Ending Balance	49	24
Assets of Managed Investment Entities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Financial assets, Beginning Balance	40	44
Total realized/unrealized gains (losses) included in Net income	(4)
Purchases and issuances		12
Sales and Settlements		(3)
Transfer into Level 3		14
Transfer out of Level 3	(6)	(3)
Financial assets, Ending Balance	$ 30	$ 64