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Investment Securities - Additional Information (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2021
Dec. 31, 2020
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Investments, Debt and Equity Securities [Abstract]            
Security Owned and Pledged as Collateral, Fair Value $ 19,600 $ 16,500 $ 19,600   $ 19,600  
Securities Received as Collateral $ 1 $ 1 1   1  
Proceeds from sales     1,100 $ 668 1,735 $ 812
Debt Securities, Available-for-sale, Realized Gain     $ 2 $ 25 $ 6 $ 25
Available-for-sale securities | Government Contracts Concentration Risk | US Treasury and Agency securities            
Concentration Risk [Line Items]            
Percentage of portfolio 96.00% 96.00%