Investments - 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, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Investment income summary:
Interest on fixed maturities	$ 103	$ 106	$ 205	$ 212
Dividends on equity securities	30	27	57	53
Other investment income	0	1	1	2
Total	133	134	263	267
Less investment expenses	2	2	4	4
Total	131	132	259	263
Realized investment gains and losses summary:
Other	(2)	3	(5)	5
Realized gains on investments	14	6	55	19
Change in unrealized gains and losses summary:
Unrealized gains (losses) on investments available-for-sale	(159)	(34)	73	114
Adjustment to deferred acquisition costs and life policy reserves	26	(8)	29	(15)
Amortization of pension actuarial loss and prior service cost	3	1	5	3
Other	(2)	3	(5)	5
Income taxes on above	76	20	49	59
Other comprehensive income (loss), net of tax	(141)	(37)	92	109
Fixed Maturities
Realized investment gains and losses summary:
Gross realized gains	2	13	4	16
Gross realized losses	0	0	0	0
Other-than-temporary impairments	0	0	2	0
Change in unrealized gains and losses summary:
Unrealized gains (losses) on investments available-for-sale	(282)	29	(307)	78
Equity Securities
Realized investment gains and losses summary:
Gross realized gains	12	6	49	29
Gross realized losses	0	(1)	0	1
Other-than-temporary impairments	0	(14)	0	30
Securities with embedded derivatives	0	1	1	5
Other	0	1	3	0
Realized gains on investments	14	6
Change in unrealized gains and losses summary:
Unrealized gains (losses) on investments available-for-sale	38	(82)	419	97
Other	$ 0	$ 1	$ 3	$ 0