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, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Investment income summary:
Interest	$ 111	$ 110	$ 222	$ 219
Dividends	42	41	81	78
Other	1	0	2	1
Total	154	151	305	298
Less investment expenses	3	2	5	4
Total	151	149	300	294
Realized investment gains and losses summary:
Realized investment gains and losses, net	(11)	44	149	105
Change in unrealized gains and losses summary:
Fixed maturities	144	186	229	376
Income tax (provision) benefit	(77)	(103)	(123)	(203)
Fixed Maturities
Realized investment gains and losses summary:
Gross realized gains	3	4	13	7
Gross realized losses	0	0	0	(1)
Other-than-temporary impairments	(6)	0	(6)	(2)
Change in unrealized gains and losses summary:
Fixed maturities	76	178	110	294
Equity Securities
Realized investment gains and losses summary:
Gross realized gains	6	38	159	100
Gross realized losses	(10)	0	(14)	(1)
Other-than-temporary impairments	(3)	0	(3)	0
Other	(1)	2	0	2
Change in unrealized gains and losses summary:
Fixed maturities	$ 145	$ 111	$ 242	$ 285