Fair Value Measurements (Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 25	$ 31
Total gains or losses (realized/unrealized):
Included in other comprehensive income	4
Purchases	1	16
Sales	(6)	(1)
Transfers into Level 3	1	11
Transfers out of Level 3	(20)	(32)
Ending balance	5	25
Corporate Fixed Maturities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	18	20
Total gains or losses (realized/unrealized):
Included in other comprehensive income	2
Purchases		16
Sales	(4)
Transfers into Level 3	1	10
Transfers out of Level 3	(14)	(28)
Ending balance	3	18
States, Municipalities And Political Subdivisions [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	3	4
Total gains or losses (realized/unrealized):
Sales	(2)	(1)
Ending balance	1	3
Preferred Stock [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	4	5
Total gains or losses (realized/unrealized):
Included in other comprehensive income	2
Purchases	1
Transfers into Level 3		1
Transfers out of Level 3	(6)	(2)
Ending balance	1	4
Taxable Fixed Maturities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance		2
Total gains or losses (realized/unrealized):
Transfers out of Level 3		$ (2)