Investment Income And Gains And Losses (Change In Net Unrealized Gains/Losses) (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2012	Dec. 31, 2011
Change in Net Unrealized Gains Losses [Line Items]
Total	$ 311	$ 380
Deferred income tax charged (credited)	104	122
Change in unrealized gains (losses), net	207	258
Fixed-Maturity Investments [Member]
Change in Net Unrealized Gains Losses [Line Items]
Total	294	386
Total Other Investments [Member]
Change in Net Unrealized Gains Losses [Line Items]
Total	$ 17	$ (6)