Investments - Realized Investment Gains and Losses and Change in Unrealized Investment Gains and Losses and Other Items (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Investment income summary:
Interest	$ 106	$ 103	$ 211	$ 207
Dividends	35	34	71	66
Other	1	1	1	2
Total	142	138	283	275
Less investment expenses	2	2	4	4
Total	140	136	279	271
Realized investment gains and losses summary:
Realized investment gains, net	60	14	107	36
Change in unrealized gains and losses summary:
Fixed maturities	(207)	153	(235)	229
Less income taxes	112	(82)	(127)	123
Fixed Maturities
Realized investment gains and losses summary:
Gross realized gains	7	4	10	6
Gross realized losses	0	(3)	0	(4)
Other-than-temporary impairments	(3)	0	(3)	0
Change in unrealized gains and losses summary:
Fixed maturities	(184)	93	(138)	181
Equity Securities
Realized investment gains and losses summary:
Gross realized gains	56	16	100	34
Gross realized losses	0	0	(1)	0
Other-than-temporary impairments	(1)	0	(1)	(1)
Other	1	(3)	2	1
Change in unrealized gains and losses summary:
Fixed maturities	$ (135)	$ 142	$ (224)	$ 171