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Regulatory Matters Regulatory Matters - Narrative (Details) - USD ($)
$ in Millions
9 Months Ended 12 Months Ended
Sep. 30, 2018
Dec. 31, 2020
Dec. 31, 2019
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]      
Cash dividends paid to parent company $ 360.0 $ 20.0  
Subsidiaries [Member]      
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]      
Cash held by Bank     $ 93.8