Invested Assets - Fair Value and Amortized Cost of Fixed Maturities by Contractual Maturity (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Schedule of Available-For-Sale Securities [Line Items]
Due in one year or less, Fair Value	$ 2,174
Due after one year through five years, Fair Value	14,525
Due after five years through ten years, Fair Value	11,494
Due after ten years, Fair Value	8,023
Subtotal fixed maturities, Fair Value	36,216
Total fixed maturities, Fair Value	38,216	38,076
Due in one year or less, Amortized Cost	2,148
Due after one year through five years, Amortized Cost	13,758
Due after five years through ten years, Amortized Cost	10,458
Due after ten years, Amortized Cost	7,471
Subtotal fixed maturities, Amortized Cost	33,835
Total fixed maturities, Amortized Cost	35,734	35,398
Residential mortgage-backed securities [Member]
Schedule of Available-For-Sale Securities [Line Items]
Taxable, Fair Value	406
Taxable, Amortized Cost	374
Commercial mortgage-backed securities [Member]
Schedule of Available-For-Sale Securities [Line Items]
Taxable, Fair Value	1,594
Taxable, Amortized Cost	$ 1,525