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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Investment income:
Interest	$ 111	$ 112	$ 222	$ 222
Dividends	50	44	96	86
Other	2	1	5	2
Total	163	157	323	310
Less investment expenses	3	3	6	6
Total	160	154	317	304
Gain (Loss) on Sale of Investments			1,022	(90)
Investment gains and losses, net:
Investment gains and losses, net	364	105	1,027	(86)
Equity securities
Investment income:
Gain (Loss) on Sale of Investments	11	4	23	7
Unrealized Gain (Loss) on Investments	355	101	999	(97)
Investment gains and losses, net:
Other	(1)	(2)	4	(2)
Investment gains and losses, net	366	105	1,022	(90)
Fixed maturities
Investment gains and losses, net:
Gross realized gains	1	3	3	7
Available-for-sale Securities, Gross Realized Losses	(2)	(1)	(2)	(1)
Investment gains and losses, net	$ (1)	$ 2	$ 1	$ 6