Fair Value Measurements - Additional Information (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($)	Mar. 31, 2019	Dec. 31, 2019 USD ($)
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Fair Value Assets, Level 1 to Level 2 Transfers, Number	0	0
Derivative Credit Risk Valuation Adjustment, Derivative Liabilities	$ 0		$ 0
Other investments	363		478
Derivative liabilities	$ 138		$ 90
Weighted average discounted rate of estimated future premium payments to be paid by the VIEs	2.20%		2.40%
Fair Value Assets, Level 2 to Level 1 Transfers, Number	0	0
Fair Value Assets, Level 2 to Level 3 Transfers, Number	0	0
Fair Value Assets, Level 3 to Level 2 Transfers, Number	0	0
Fair Value Measured at Net Asset Value Per Share [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Other investments	$ 232		$ 296
Fixed Income Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Percentage of investment portfolio valued using dealer quotes	4.00%		4.00%
Minimum [Member] | Fixed Income Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Percentage of investment portfolio valued using internal valuation models	2.00%		2.00%
Maximum [Member] | Fixed Income Securities [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Percentage of investment portfolio valued using external pricing services	94.00%		94.00%
Variable Interest Entity [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Weighted average discounted rate of estimated future premium payments to be paid by the VIEs	2.50%		2.70%
Variable Interest Entity, Primary Beneficiary [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Derivative liabilities	$ 1,610		$ 1,657