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		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Realized investment gains and losses summary:
Securities with embedded derivatives	$ 1		$ 5	$ 4
Other	1	2		2
Total	6	67	19	79
Change in unrealized gains and losses summary:
Available for sale	(47)	142	194	284
Adjustment to deferred acquisition costs and life policy reserves	(8)	(4)	(15)	(4)
Amortization of pension actuarial loss and prior service cost	1	1	3	2
Other	(5)	(2)	(10)	(1)
Income taxes on above	20	(26)	(59)	(72)
Total	(37)	48	109	134
Debt Securities
Realized investment gains and losses summary:
Gross realized gains	13	4	16	7
Change in unrealized gains and losses summary:
Available for sale	29	96	78	104
Equity Securities
Realized investment gains and losses summary:
Gross realized gains	6	79	29	114
Gross realized losses	(1)	(18)	(1)	(18)
Other-than-temporary impairments	(14)		(30)	(30)
Change in unrealized gains and losses summary:
Available for sale	(82)	(21)	97	101
Other Investments
Change in unrealized gains and losses summary:
Other	$ 3	$ 2	$ 5	$ 3