Invested Assets and Related Income - Fair Value and Amortized Cost of Fixed Maturities by Contractual Maturity (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Schedule of Available-For-Sale Securities [Line Items]
Due in one year or less, Fair value	$ 2,213
Due after one year through five years, Fair value	14,212
Due after five years through ten years, Fair value	11,594
Due after ten years, Fair value	7,878
Subtotal fixed maturities,Fair Value	35,897
Total fixed maturities, Fair value	38,076	37,184
Due in one year or less, Amortized cost	2,185
Due after one year through five years, Amortized cost	13,439
Due after five years through ten years, Amortized cost	10,470
Due after ten years, Amortized cost	7,234
Subtotal fixed maturities, Amortized Cost	33,328
Total fixed maturities, Amortized Cost	35,398	34,762
Residential mortgage-backed securities [Member]
Schedule of Available-For-Sale Securities [Line Items]
Taxable, Fair value	455
Taxable, Amortized cost	421
Commercial mortgage-backed securities [Member]
Schedule of Available-For-Sale Securities [Line Items]
Taxable, Fair value	1,724
Taxable, Amortized cost	$ 1,649