Investments - (Summary of Allowance for Credit Losses on HTM Investments) (Detail) - Variable Interest Entity Primary Beneficiary [Member] $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($)
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items]
Beginning balance	$ 0
Ending balance	46
Accounting Standards Update 2016-13 [Member]
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items]
Beginning balance	37
Current period provision for expected credit losses	9
Initial allowance recognized for PCD assets	0
Write- Offs	0
Recoveries	0
Ending balance	46
Corporate Obligations [Member]
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items]
Ending balance	46
Corporate Obligations [Member] | Accounting Standards Update 2016-13 [Member]
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items]
Beginning balance	37
Current period provision for expected credit losses	9
Initial allowance recognized for PCD assets	0
Write- Offs	0
Recoveries	0
Ending balance	$ 46