Invested Assets and Related Income - Fair Value and Amortized Cost of Foreign Government and Government Agency Fixed Maturities (Detail) (Foreign government and government agency obligations [Member], USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Canada [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	$ 2,157	$ 2,075
Amortized Cost	2,060	1,943
Germany [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	1,127	897
Amortized Cost	1,070	855
United Kingdom [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	1,024	1,275
Amortized Cost	939	1,145
Australia [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	742	623
Amortized Cost	663	579
Brazil [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fair Value	310	334
Amortized Cost	$ 310	$ 334