Pretax Other-Than-Temporary Impairment Losses by Investment Category (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]
Other-than-temporary impairment losses	$ 1,901	[1]	$ 459	[2]	$ 1,361	[2]
Perpetual Securities
Gain (Loss) on Investments [Line Items]
Other-than-temporary impairment losses	565		160		729
Corporate Bonds
Gain (Loss) on Investments [Line Items]
Other-than-temporary impairment losses	1,316		285		458
Collateralized Debt Obligations
Gain (Loss) on Investments [Line Items]
Other-than-temporary impairment losses	0		0		148
Mortgage- and asset-backed Securities
Gain (Loss) on Investments [Line Items]
Other-than-temporary impairment losses	17		12		24
Municipalities
Gain (Loss) on Investments [Line Items]
Other-than-temporary impairment losses	2		0		0
Equity Securities
Gain (Loss) on Investments [Line Items]
Other-than-temporary impairment losses	$ 1		$ 2		$ 2

[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