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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Investment income:
Interest	$ 113	$ 110	$ 339	$ 332
Dividends	55	50	161	146
Other	2	5	7	10
Total	170	165	507	488
Less investment expenses	3	4	9	10
Total	167	161	498	478
Gain (Loss) on Sale of Investments			(137)	1,103
Investment gains and losses, net:
Investment gains and losses, net	533	86	(132)	1,113
Equity securities
Investment income:
Gain (Loss) on Sale of Investments	55	0	75	27
Unrealized Gain (Loss) on Investments	475	89	(130)	1,084
Investment gains and losses, net:
Other	0	(2)	(5)	2
Investment gains and losses, net	530	89	(55)	1,111
Fixed maturities
Investment gains and losses, net:
Gross realized gains	4	6	9	9
Writedown of Impaired Securities Intended to be Sold	(1)		(78)
Other-than-temporary impairment		(6)		(6)
Investment gains and losses, net	3	(1)	(72)	0
Available-for-sale Securities, Gross Realized Losses	$ 0	$ (1)	$ (3)	$ (3)