Carrying Values and Estimated Fair Values of Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Assets:
Equity securities	$ 25	$ 23
Investments other than Consolidated Variable Interest Entities
Assets:
Perpetual securities	5,149	5,974
Variable Interest Entity, Consolidated
Assets:
Interest rate, foreign currency, and credit default swaps	375	564
Perpetual securities	1,290	1,538
Carrying Value
Assets:
Equity securities	25	23
Interest rate, foreign currency, and credit default swaps	375	564
Liabilities:
Notes payable (excluding capitalized leases)	3,275	3,032
Interest rate, foreign currency, and credit default swaps	531	741
Obligation to Japanese policyholder protection corporation	71	108
Carrying Value | Investments other than Consolidated Variable Interest Entities
Assets:
Fixed-maturity securities	88,588	72,570
Perpetual securities	5,149	5,974
Carrying Value | Variable Interest Entity, Consolidated
Assets:
Fixed-maturity securities	5,993	5,869
Perpetual securities	1,290	1,538
Fair Value
Assets:
Equity securities	25	23
Interest rate, foreign currency, and credit default swaps	375	564
Liabilities:
Notes payable (excluding capitalized leases)	3,536	3,248
Interest rate, foreign currency, and credit default swaps	531	741
Obligation to Japanese policyholder protection corporation	71	108
Fair Value | Investments other than Consolidated Variable Interest Entities
Assets:
Fixed-maturity securities	88,039	72,999
Perpetual securities	5,149	5,974
Fair Value | Variable Interest Entity, Consolidated
Assets:
Fixed-maturity securities	5,916	5,825
Perpetual securities	$ 1,290	$ 1,538