Investments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2012 Investment	Dec. 31, 2011
Gain (Loss) on Investments [Line Items]
Unrealized investment gains due to a net gain position	$ 1,725	$ 1,542
Fixed maturities, fair value of hybrid securities	56
Other-than-temporary impairment charges	0	0
Impaired securities	5
Investments securities total unrealized loss in an unrealized loss position for 12 months or more	3	5
Procter And Gamble Company And Exxon Mobile Corporation
Gain (Loss) on Investments [Line Items]
Unrealized investment gains due to a net gain position	281
Two Primary Contributors
Gain (Loss) on Investments [Line Items]
Number of securities	3
Debt Securities
Gain (Loss) on Investments [Line Items]
Unrealized investment gains due to a net gain position	750	713
Number of securities total unrealized loss in an unrealized loss position for 12 months or more	14	20
Investments securities total unrealized loss in an unrealized loss position for 12 months or more	3	5
Debt Securities | Minimum
Gain (Loss) on Investments [Line Items]
Percentage of investment amortized cost	70.00%	70.00%
Equity Securities
Gain (Loss) on Investments [Line Items]
Unrealized investment gains due to a net gain position	975	829
Number of securities total unrealized loss in an unrealized loss position for 12 months or more	1	2
Equity Securities | Minimum
Gain (Loss) on Investments [Line Items]
Percentage of investment amortized cost	70.00%	70.00%
Equity Securities | Maximum
Gain (Loss) on Investments [Line Items]
Investments securities total unrealized loss in an unrealized loss position for 12 months or more	$ 1	$ 1