Investments - Additional Information (Detail) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2020 USD ($) security	Jun. 30, 2019 security	Jun. 30, 2020 USD ($) security	Jun. 30, 2019 security	Dec. 31, 2019 USD ($) security
Gain (Loss) on Securities
Debt Securities, Available-for-sale, Allowance for Credit Loss	0		0
Equity securities, at fair value | $	$ 7,317		$ 7,317		$ 7,752
Largest Single Common Stock Holding | $	$ 514		$ 514
Largest equity holdings to total equity portfolio	7.30%		7.30%
Largest equity holdings to total portfolio	2.70%		2.70%
Number Of Securities Other Than Temporary Impairment Losses1		0
Fixed maturity investments, Percentage of amortized costs			70.00%		70.00%
Fixed maturities
Gain (Loss) on Securities
Number Of Impaired Securities Intended to be Sold	0		12
Number Of Securities Other Than Temporary Impairment Losses1				0
Number Of Securities Continuous Unrealized Loss Position	242		242
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss 3 | $	$ 53		$ 53		$ 7
Number Of Securities Continuous Unrealized Loss Position More Than Twelve Months					38
Unrealized losses 12 months or more (equity investment less than $500,000) | $	$ (2)		$ (2)		$ (3)
Number Of Securities Continuous Unrealized Loss Position and Below 70 Percent of Amortized Cost	5		5
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 | $	$ 7,082		$ 7,082		$ 7,518