Information Regarding Pretax Realized Gains and Losses From Investments (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Gain (Loss) on Investments [Line Items]
Derivative gains (losses)	$ (224,000,000)	$ 14,000,000	$ (279,000,000)	$ (72,000,000)
Other-than-temporary impairment losses	(166,000,000)	(13,000,000)	(1,100,000,000)	(55,000,000)
Total realized investment gains (losses)	(83,000,000)	9,000,000	(1,330,000,000)	(127,000,000)
Debt Securities
Gain (Loss) on Investments [Line Items]
Gross gains from sales	354,000,000	25,000,000	458,000,000	75,000,000
Gross losses from sales	(56,000,000)	(17,000,000)	(375,000,000)	(207,000,000)
Net gains (losses) from redemptions	9,000,000	0	15,000,000	1,000,000
Total realized investment gains (losses)	263,000,000	(4,000,000)	(695,000,000)	(143,000,000)
Debt Securities | Available-for-sale Securities
Gain (Loss) on Investments [Line Items]
Other-than-temporary impairment losses	(44,000,000)	(12,000,000)	(793,000,000)	(12,000,000)
Perpetual Securities
Gain (Loss) on Investments [Line Items]
Gross gains from sales	0	0	54,000,000	133,000,000
Gross losses from sales	0	0	(109,000,000)	0
Other-than-temporary impairment losses	(122,000,000)	0	(306,000,000)	(41,000,000)
Total realized investment gains (losses)	(122,000,000)	0	(361,000,000)	92,000,000
Equity Securities
Gain (Loss) on Investments [Line Items]
Gross losses from sales	0	0	0	(2,000,000)
Other-than-temporary impairment losses	0	(1,000,000)	(1,000,000)	(2,000,000)
Total realized investment gains (losses)	0	(1,000,000)	(1,000,000)	(4,000,000)
Other Assets:
Gain (Loss) on Investments [Line Items]
Derivative gains (losses)	(224,000,000)	14,000,000	(291,000,000)	(72,000,000)
Other	0	0	18,000,000	0
Total realized investment gains (losses)	$ (224,000,000)	$ 14,000,000	$ (273,000,000)	$ (72,000,000)