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, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Investment income summary:
Interest	$ 108	$ 105	$ 319	$ 312
Dividends	37	35	108	101
Other	1	0	2	2
Total	146	140	429	415
Less investment expenses	3	2	7	6
Total	143	138	422	409
Realized investment gains and losses summary:
Realized investment gains, net	3	65	110	101
Change in unrealized gains and losses summary:
Fixed maturities	(238)	(78)	(473)	151
Less income taxes	127	42	(254)	81
Fixed Maturities
Realized investment gains and losses summary:
Gross realized gains	4	6	14	12
Gross realized losses	0	0	0	(4)
Other-than-temporary impairments	(8)	0	(11)	0
Change in unrealized gains and losses summary:
Fixed maturities	(15)	(66)	(153)	115
Equity Securities
Realized investment gains and losses summary:
Gross realized gains	6	59	106	93
Gross realized losses	0	0	(1)	0
Other-than-temporary impairments	0	0	(1)	(1)
Other	1	0	3	1
Change in unrealized gains and losses summary:
Fixed maturities	$ (350)	$ (54)	$ (574)	$ 117