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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Investment income:
Interest	$ 110	$ 111	$ 332	$ 333
Dividends	50	45	146	131
Other	5	1	10	3
Total	165	157	488	467
Less investment expenses	4	3	10	9
Total	161	154	478	458
Gain (Loss) on Sale of Investments			1,103	367
Investment gains and losses, net:
Investment gains and losses, net	86	458	1,113	372
Equity securities
Investment income:
Gain (Loss) on Sale of Investments	0	8	27	17
Unrealized Gain (Loss) on Investments	89	450	1,084	351
Investment gains and losses, net:
Other	(2)	(1)	2	(3)
Investment gains and losses, net	89	458	1,111	368
Fixed maturities
Investment gains and losses, net:
Gross realized gains	6	2	9	9
Available-for-sale Securities, Gross Realized Losses	(1)	(1)	(3)	(2)
Other-than-temporary impairment	(6)	0	(6)	0
Investment gains and losses, net	$ (1)	$ 1	$ 0	$ 7