Investments - Realized Investment Gains and Losses and Change in Unrealized Investment Gains and Losses and Other Items (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Investment income summary:
Interest	$ 111	$ 109
Dividends	39	37
Other	1	1
Total	151	147
Less investment expenses	2	2
Total	149	145
Realized investment gains and losses summary:
Realized investment gains, net	160	61
Change in unrealized gains and losses summary:
Fixed maturities	85	190
Income tax (provision) benefit	(46)	(100)
Fixed Maturities
Realized investment gains and losses summary:
Gross realized gains	10	3
Gross realized losses	0	(1)
Other-than-temporary impairments	0	(2)
Change in unrealized gains and losses summary:
Fixed maturities	34	116
Equity Securities
Realized investment gains and losses summary:
Gross realized gains	153	62
Gross realized losses	(4)	(1)
Other-than-temporary impairments	0	0
Other	1	0
Change in unrealized gains and losses summary:
Fixed maturities	$ 97	$ 174