Investments - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Investment [Line Items]
Written down securities carried at fair value	$ 48,000,000
Balances related to bifurcated credit loss positions included in other comprehensive income	22,000,000	22,000,000	22,000,000
Unrealized gain (loss) on investments	1,600,000,000	964,000,000	108,000,000	(455,000,000)
Total issues of fixed-maturities and equities	1,630	1,373
Estimated fair value of mortgage loans	500,000	600,000
Accumulated depreciation on investment real estate	2,100,000	1,800,000
Non-income producing fixed maturities at book value	125,000
Non-income producing fixed maturities at fair value	150,000
Non-income producing investment real estate	2,600,000
Collateral Loans
Investment [Line Items]
Other investments		7,000,000
Financial Sector
Investment [Line Items]
Unrealized gain (loss) on investments	339,000,000	14,000,000
Other Sectors
Investment [Line Items]
Unrealized gain (loss) on investments	$ 1,200,000,000	$ 950,000,000