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Securities - Summary of Gross Proceeds and Gross Realized Gains and Losses from Sale of Available-for-Sale Securities (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Investments Debt And Equity Securities [Abstract]    
Gross proceeds $ 484 $ 361
Gross realized gains 2 $ 5
Gross realized losses $ 1