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
	Mar. 31, 2013	Mar. 31, 2012
Investment income summary:
Interest on fixed maturities	$ 102	$ 106
Dividends on equity securities	27	26
Other investment income	1	1
Total	130	133
Less investment expenses	2	2
Total	128	131
Realized investment gains and losses summary:
Other	(3)	2
Realized gains on investments	41	13
Change in unrealized gains and losses summary:
Unrealized gains (losses) on investments available-for-sale	232	148
Adjustment to deferred acquisition costs and life policy reserves	3	(7)
Amortization of pension actuarial loss and prior service cost	2	2
Other	(3)	2
Income taxes on above	(125)	(79)
Other comprehensive income, net of tax	233	146
Fixed Maturities
Realized investment gains and losses summary:
Gross realized gains	2	3
Gross realized losses	0	0
Other-than-temporary impairments	(2)	0
Change in unrealized gains and losses summary:
Unrealized gains (losses) on investments available-for-sale	(25)	49
Equity Securities
Realized investment gains and losses summary:
Gross realized gains	37	23
Gross realized losses	0	0
Other-than-temporary impairments	0	(16)
Securities with embedded derivatives	1	4
Other	3	(1)
Realized gains on investments	41	13
Change in unrealized gains and losses summary:
Unrealized gains (losses) on investments available-for-sale	381	179
Other	$ 3	$ (1)