Investment Income, Realized Investment Gains and Losses and Change in Unrealized Investment Gains and Losses (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Investment income summarized by investment category:
Interest on fixed maturities	$ 424	$ 423	$ 402
Dividends on equity securities	104	99	100
Other investment income	4	4	7
Total	532	526	509
Less investment expenses	7	8	8
Total	525	518	501
Realized investment gains and losses summary:
Securities with embedded derivatives	(1)	10	27
Other	6	(2)	(7)
Total	70	159	336
Change in unrealized investment gains and losses and other summary:
Adjustment to deferred acquisition costs and life policy reserves	(14)	(9)	(24)
Pension obligations	(25)	3	(14)
Income taxes on above	(71)	(78)	(207)
Total	132	145	383
Available for sale	309	387	936
Debt Securities
Realized investment gains and losses summary:
Gross realized gains	11	25	15
Gross realized losses	0	(12)	(30)
Other-than-temporary impairments	(5)	(3)	(62)
Change in unrealized investment gains and losses and other summary:
Available for sale	200	154	734
Equity Securities
Realized investment gains and losses summary:
Gross realized gains	151	174	624
Gross realized losses	(40)	0	(162)
Other-than-temporary impairments	(52)	(33)	(69)
Change in unrealized investment gains and losses and other summary:
Available for sale	39	70	(134)
Other Investments
Change in unrealized investment gains and losses and other summary:
Other	$ 3	$ 5	$ 28