Invested Assets and Related Income - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014 Investment	Dec. 31, 2013
Schedule of Available-For-Sale Securities [Line Items]
Fixed maturities, Fair Value	$ 38,780	$ 37,091
Approximate number of individual fixed maturities in unrealized loss position	735
Approximate number of individual equity securities in unrealized loss position	15
Cumulative credit-related losses recognized in net income	18	20
Taxable [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fixed maturities, Fair Value	19,008	18,670
Taxable [Member] | Supranational Organization Issued [Member]
Schedule of Available-For-Sale Securities [Line Items]
Fixed maturities, Fair Value	$ 469	$ 547