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Available-for-Sale Debt Securities - Additional Information (Details)
$ in Millions
3 Months Ended
Mar. 31, 2020
USD ($)
position
Dec. 31, 2019
USD ($)
Debt Securities, Available-for-sale [Abstract]    
Accrued Interest Receivable $ 60 $ 37
Securities in Unrealized Loss Positions, Number of Positions (Securities) | position 873  
Credit Losses for Available-for-Sale Debt Securities $ 0  
Write-offs in Accrued Interest Receivable $ 0