Realized Investment Gains and Losses and Change in Unrealized Investment Gains and Losses and Other Items (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Realized investment gains and losses summary:
Securities with embedded derivatives	$ (4)	$ (4)	$ 1
Other	1	2	1	4
Total	10	(2)	29	77
Change in unrealized gains and losses summary:
Available for sale	263	(305)	457	(21)
Adjustment to deferred acquisition costs and life policy reserves	(6)	(7)	(21)	(11)
Amortization of pension actuarial loss and prior service cost	2	1	5	3
Other	(6)	(6)	(16)	(7)
Income taxes on above	(88)	108	(147)	36
Total	161	(200)	270	(66)
Debt Securities
Realized investment gains and losses summary:
Gross realized gains	14	2	30	9
Other-than-temporary impairments		(3)		(3)
Change in unrealized gains and losses summary:
Available for sale	110	76	188	180
Equity Securities
Realized investment gains and losses summary:
Gross realized gains	1	18	30	132
Gross realized losses		(17)	(1)	(35)
Other-than-temporary impairments	(2)		(32)	(30)
Change in unrealized gains and losses summary:
Available for sale	143	(379)	240	(278)
Other Investments
Change in unrealized gains and losses summary:
Other		$ 1	$ 5	$ 4

Other Comprehensive Income, Unrealized gains losses on deferred acquisition costs , Period Increase (Decrease)

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