Invested Assets - Fair Value and Amortized Cost of Fixed Maturities by Contractual Maturity (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Schedule of Available-For-Sale Securities [Line Items]
Due in one year or less, Fair value	$ 2,476
Due after one year through five years, Fair value	13,280
Due after five years through ten years, Fair value	12,299
Due after ten years, Fair value	7,871
Subtotal fixed maturities, Fair Value	35,926
Total fixed maturities, Fair Value	38,217	37,184
Due in one year or less, Amortized cost	2,447
Due after one year through five years, Amortized cost	12,550
Due after five years through ten years, Amortized cost	11,039
Due after ten years, Amortized cost	7,178
Total Due, Amortized Cost	33,214
Total fixed maturities, Amortized Cost	35,384	34,762
Residential mortgage-backed securities [Member]
Schedule of Available-For-Sale Securities [Line Items]
Taxable, Fair value	527
Taxable, Amortized cost	491
Commercial mortgage-backed securities [Member]
Schedule of Available-For-Sale Securities [Line Items]
Taxable, Fair value	1,764
Taxable, Amortized cost	$ 1,679