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Fair Value (Narrative) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Fair Value Disclosure [Line Items]    
Transfers between Fair Value Hierarchies $ 0.0 $ 0.0
Allowance for Credit Loss 0.6 (0.9)
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Period Increase (Decrease) 0.0  
Debt Securities, Available-for-Sale, Realized Gain (Loss) (1.0)  
U.S. Treasury debt securities    
Fair Value Disclosure [Line Items]    
Allowance for Credit Loss 0.0 0.0
Available-for-sale securities, maturities of less than a year 16.8  
Corporate/Other debt securities    
Fair Value Disclosure [Line Items]    
Allowance for Credit Loss 0.6 $ (0.9)
Available-for-sale securities, maturities of less than a year $ 4.9