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Off-Balance Sheet Credit Risk (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 13, 2018
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]      
General settlement period of securities transactions 2 days    
Fair value of securities accepted as collateral permitted to sell or repledge $ 2,300.0 $ 2,400.0  
Fair value of collateral securities sold or repledged 391.6 535.4  
Outstanding commitments to originate loans 384.5 146.7  
Letters of credit outstanding 38.3 $ 26.3  
Unused Lines Of Credit [Member]      
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]      
Unused lines of credit to commercial and consumer borrowers $ 1,500.0   $ 919.5
Standby Letters of Credit [Member] | Maximum [Member]      
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]      
Letters of credit, expiration period 1 year