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Investment Securities (Narrative) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2022
Dec. 31, 2023
Schedule of Investments [Line Items]    
Net unsettled investment purchases $ 200.0 $ 100.0
Transferred securities at fair value from available for sale to held to maturity 82,700.0  
Unrealized losses related to transfers (5,100.0) (4,200.0)
Investment securities, allowance for credit loss 149.0 92.0
Pretax loss from derivatives 314.0 293.0
US Treasury and Government [Member]    
Schedule of Investments [Line Items]    
Transferred securities at fair value from available for sale to held to maturity 34,000.0  
Residential mortgage-backed Securities | Mortgage-backed Securities Agency    
Schedule of Investments [Line Items]    
Transferred securities at fair value from available for sale to held to maturity 39,000.0  
Asset-backed Securities    
Schedule of Investments [Line Items]    
Transferred securities at fair value from available for sale to held to maturity 6,300.0  
Other debt    
Schedule of Investments [Line Items]    
Transferred securities at fair value from available for sale to held to maturity $ 3,400.0  
Federal National Mortgage Association Certificates and Obligations (FNMA)    
Schedule of Investments [Line Items]    
Amortized cost of debt securities of a single issuer that exceeds 10 percent of shareholders equity   37,300.0
Fair value of debt securities of a single issuer that exceeds 10 percent of shareholders equity   34,600.0
Federal Home Loan Mortgage Corp (FHLMC)    
Schedule of Investments [Line Items]    
Amortized cost of debt securities of a single issuer that exceeds 10 percent of shareholders equity   32,100.0
Fair value of debt securities of a single issuer that exceeds 10 percent of shareholders equity   $ 30,000.0