v3.25.1
Derivative Financial Instruments Location of Gains and Losses Designated as Hedging Instruments, Consolidated Statements of Income (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Derivative Instruments, Gain (Loss)    
Net Investment Income $ 513.2 $ 513.5
Net Investment Gain (Loss) (206.8) (1.2)
Interest and Debt Expense 52.0 49.5
Net Gain (Loss) on Derivatives (5.3) 1.6
Designated as Hedging Instrument | Interest Rate Swaps | Net Investment Income | Cash Flow Hedging    
Derivative Instruments, Gain (Loss)    
Net Investment Income 17.4 47.6
Net Gain (Loss) on Derivatives 2.6 6.0
Designated as Hedging Instrument | Interest Rate Swaps | Net Investment Gain (Loss) | Cash Flow Hedging    
Derivative Instruments, Gain (Loss)    
Net Investment Gain (Loss) (0.4) 0.0
Net Gain (Loss) on Derivatives 0.4 0.0
Designated as Hedging Instrument | Interest Rate Swaps | Interest and Debt Expense | Cash Flow Hedging    
Derivative Instruments, Gain (Loss)    
Interest and Debt Expense 0.0 0.7
Net Gain (Loss) on Derivatives 0.0 0.0
Designated as Hedging Instrument | Foreign Exchange Contracts | Net Investment Income | Cash Flow Hedging    
Derivative Instruments, Gain (Loss)    
Net Investment Income 2.3 2.2
Net Gain (Loss) on Derivatives (0.7) (0.5)
Designated as Hedging Instrument | Foreign Exchange Contracts | Net Investment Income | Fair Value Hedging    
Derivative Instruments, Gain (Loss)    
Net Investment Income 4.4 4.2
Net Gain (Loss) on Derivatives (5.2) 3.1
Designated as Hedging Instrument | Foreign Exchange Contracts | Net Investment Gain (Loss) | Cash Flow Hedging    
Derivative Instruments, Gain (Loss)    
Net Investment Gain (Loss) 0.0 0.0
Net Gain (Loss) on Derivatives 0.0 0.0
Designated as Hedging Instrument | Foreign Exchange Contracts | Net Investment Gain (Loss) | Fair Value Hedging    
Derivative Instruments, Gain (Loss)    
Net Investment Gain (Loss) 21.5 (17.6)
Net Gain (Loss) on Derivatives (21.5) 17.6
Designated as Hedging Instrument | Foreign Exchange Contracts | Interest and Debt Expense | Cash Flow Hedging    
Derivative Instruments, Gain (Loss)    
Interest and Debt Expense 0.0 0.0
Net Gain (Loss) on Derivatives 0.0 0.0
Designated as Hedging Instrument | Foreign Exchange Contracts | Interest and Debt Expense | Fair Value Hedging    
Derivative Instruments, Gain (Loss)    
Interest and Debt Expense 0.0 0.0
Net Gain (Loss) on Derivatives 0.0 0.0
Designated as Hedging Instrument | Forwards | Net Investment Income | Cash Flow Hedging    
Derivative Instruments, Gain (Loss)    
Net Investment Income 12.3 9.0
Net Gain (Loss) on Derivatives (0.4) (0.2)
Designated as Hedging Instrument | Forwards | Net Investment Gain (Loss) | Cash Flow Hedging    
Derivative Instruments, Gain (Loss)    
Net Investment Gain (Loss) 0.0 0.0
Net Gain (Loss) on Derivatives 0.0 0.0
Designated as Hedging Instrument | Forwards | Interest and Debt Expense | Cash Flow Hedging    
Derivative Instruments, Gain (Loss)    
Interest and Debt Expense 0.0 0.0
Net Gain (Loss) on Derivatives $ 0.0 $ 0.0