Fair Value Measurements - Summary of Information about Described Model Inputs Used to Determine Fair Value of Each Class of Credit Derivatives (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Other investments	$ 363	$ 478
Fair value of derivative liabilities	134
Real Estate [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Other investments	15	16
Interest Rate Contract [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Other investments	57	176
Illiquid Investments [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Other investments	$ 47	$ 51
Asset-backed Securities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Inputs Coupon Rate	5.98%	5.97%
Fair Value Inputs Maturity	15 years 4 months 9 days	15 years 6 months 29 days
Fair Value Inputs Yield	13.00%	11.75%
Variable Interest Entity, Primary Beneficiary [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair value of derivative liabilities	$ 0