Claim And Claim Adjustment Expense Reserves (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Claim And Claim Adjustment Expense Reserves [Line Items]
Catastrophe losses, net of reinsurance	$ 28	$ 55
Life And Group Non-Core [Member]
Claim And Claim Adjustment Expense Reserves [Line Items]
Unfavorable (favorable) net prior year development	$ (1)	$ 7