Investments - Realized Investment Gains and Losses and Change in Unrealized Investment Gains and Losses and Other Items (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Investment income summary:
Interest	$ 111	$ 108	$ 330	$ 319
Dividends	39	37	117	108
Other	1	1	2	2
Total	151	146	449	429
Less investment expenses	3	3	7	7
Total	148	143	442	422
Realized investment gains and losses summary:
Realized investment gains, net	56	3	161	110
Change in unrealized gains and losses summary:
Fixed maturities	41	(238)	417	(473)
Income tax (provision) benefit	(21)	127	(224)	254
Fixed Maturities
Realized investment gains and losses summary:
Gross realized gains	10	4	17	14
Gross realized losses	0	0	(1)	0
Other-than-temporary impairments	0	(8)	(2)	(11)
Change in unrealized gains and losses summary:
Fixed maturities	(20)	(15)	274	(153)
Equity Securities
Realized investment gains and losses summary:
Gross realized gains	47	6	147	106
Gross realized losses	0	0	(1)	(1)
Other-than-temporary impairments	0	0	0	(1)
Other	(1)	1	1	3
Change in unrealized gains and losses summary:
Fixed maturities	$ 82	$ (350)	$ 367	$ (574)