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, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Investment income summary:
Interest	$ 110	$ 106	$ 219	$ 211
Dividends	41	35	78	71
Other	0	1	1	1
Total	151	142	298	283
Less investment expenses	2	2	4	4
Total	149	140	294	279
Realized investment gains and losses summary:
Realized investment gains, net	44	60	105	107
Change in unrealized gains and losses summary:
Fixed maturities	186	(207)	376	(235)
Less income taxes	(103)	112	(203)	127
Fixed Maturities
Realized investment gains and losses summary:
Gross realized gains	4	7	7	10
Gross realized losses	0	0	(1)	0
Other-than-temporary impairments	0	(3)	(2)	(3)
Change in unrealized gains and losses summary:
Fixed maturities	178	(184)	294	(138)
Equity Securities
Realized investment gains and losses summary:
Gross realized gains	38	56	100	100
Gross realized losses	0	0	(1)	(1)
Other-than-temporary impairments	0	(1)	0	(1)
Other	2	1	2	2
Change in unrealized gains and losses summary:
Fixed maturities	$ 111	$ (135)	$ 285	$ (224)