Information Regarding Pretax Realized Gains and Losses From Investments (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Gain (Loss) on Investments [Line Items]
Derivative gains (losses)	$ (245)		$ (1)		$ 0
Other-than-temporary impairment losses	(1,901)	[1]	(459)	[2]	(1,361)	[2]
Total realized investment gains (losses)	(1,552)		(422)		(1,212)
Debt Securities
Gain (Loss) on Investments [Line Items]
Gross gains from sales	992		117		258
Gross losses from sales	(465)		(212)		(18)
Total realized investment gains (losses)	(739)		(389)		(388)
Debt Securities | Available-for-sale Securities
Gain (Loss) on Investments [Line Items]
Net gains (losses) from redemptions	69		1		1
Other-than-temporary impairment losses	(1,335)		(297)		(630)
Debt Securities | Held-to-maturity Securities
Gain (Loss) on Investments [Line Items]
Net gains (losses) from redemptions	0		2		1
Perpetual Securities
Gain (Loss) on Investments [Line Items]
Gross gains from sales	102		133		4
Gross losses from sales	(109)		0		(101)
Other-than-temporary impairment losses	(565)		(160)		(729)
Total realized investment gains (losses)	(572)		(27)		(826)
Equity Securities
Gain (Loss) on Investments [Line Items]
Gross losses from sales	0		(2)		0
Other-than-temporary impairment losses	(1)		(2)		(2)
Total realized investment gains (losses)	(1)		(4)		(2)
Other assets
Gain (Loss) on Investments [Line Items]
Derivative gains (losses)	(257)		(1)		0
Other	17		(1)		4
Total realized investment gains (losses)	$ (240)		$ (2)		$ 4

[1] Includes $1.3 billion for credit-related impairments and $615 million from change in intent to sell securities

[2] Consisted completely of credit-related impairments