Investments - Additional Information (Detail)	3 Months Ended		12 Months Ended
	Mar. 31, 2020 USD ($) security	Mar. 31, 2019 USD ($) security	Dec. 31, 2019 USD ($) security
Gain (Loss) on Securities
Debt Securities, Available-for-sale, Allowance for Credit Loss | security	0
Equity securities, at fair value	$ 6,225,000,000		$ 7,752,000,000
Largest Single Common Stock Holding	$ 395,000,000
Largest equity holdings to total equity portfolio	6.60%
Largest equity holdings to total portfolio	2.30%
Fixed maturity investments, Percentage of amortized costs	70.00%		70.00%
Fixed maturities
Gain (Loss) on Securities
Writedown of Impaired Securities Intended to be Sold	$ (77,000,000)
Number Of Impaired Securities Intended to be Sold | security	12
Number Of Securities Other Than Temporary Impairment Losses1 | security		0
Provision for Other Credit Losses	$ 0	$ 0
Number Of Securities Continuous Unrealized Loss Position | security	605
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss 3	$ 195,000,000		$ 7,000,000
Number Of Securities Continuous Unrealized Loss Position More Than Twelve Months | security			38
Unrealized losses 12 months or more (equity investment less than $500,000)	$ (6,000,000)		$ (3,000,000)
Number Of Securities Continuous Unrealized Loss Position and Below 70 Percent of Amortized Cost	18
Number Of Securities Continuous Unrealized Loss Position More Than Twelve Months and Below 70 Percent of Amortized Cost			0
Common equities | Equity securities
Gain (Loss) on Securities
Equity securities, at fair value	$ 6,017,000,000.000		$ 7,518,000,000