Invested Assets - Fair Value and Amortized Cost of Fixed Maturities by Contractual Maturity (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Schedule of Available-For-Sale Securities [Line Items]
Due in one year or less, Fair Value	$ 2,180
Due after one year through five years, Fair Value	14,165
Due after five years through ten years, Fair Value	11,717
Due after ten years, Fair Value	7,854
Subtotal fixed maturities, Fair Value	35,916
Total fixed maturities, Fair Value	37,610	38,076
Due in one year or less, Amortized Cost	2,149
Due after one year through five years, Amortized Cost	13,581
Due after five years through ten years, Amortized Cost	11,148
Due after ten years, Amortized Cost	7,733
Subtotal fixed maturities, Amortized Cost	34,611
Total fixed maturities, Amortized Cost	36,246	35,398
Residential mortgage-backed securities [Member]
Schedule of Available-For-Sale Securities [Line Items]
Taxable, Fair Value	324
Taxable, Amortized Cost	302
Commercial mortgage-backed securities [Member]
Schedule of Available-For-Sale Securities [Line Items]
Taxable, Fair Value	1,370
Taxable, Amortized Cost	$ 1,333