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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Investment income:
Interest	$ 114	$ 111	$ 226	$ 222
Dividends	53	50	106	96
Other	2	2	5	5
Total	169	163	337	323
Less investment expenses	3	3	6	6
Total	166	160	331	317
Gain (Loss) on Sale of Investments			(669)	1,022
Investment gains and losses, net:
Investment gains and losses, net	1,060	364	(665)	1,027
Equity securities
Investment income:
Gain (Loss) on Sale of Investments	24	11	17	23
Unrealized Gain (Loss) on Investments	1,044	355	(602)	999
Investment gains and losses, net:
Other	(8)	(1)	(5)	4
Investment gains and losses, net	1,068	366	(585)	1,022
Fixed maturities
Investment gains and losses, net:
Gross realized gains	3	1	5	3
Writedown of Impaired Securities Intended to be Sold	0		(77)
Other-than-temporary impairment		0		0
Investment gains and losses, net	0	(1)	(75)	1
Available-for-sale Securities, Gross Realized Losses	$ (3)	$ (2)	$ (3)	$ (2)