Derivative Financial Instruments Location of Gains and Losses Designated as Hedging Instruments, Consolidated Statements of Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Derivative Instruments, Gain (Loss)
Net Investment Income	$ 511.6	$ 550.2	$ 1,597.8	$ 1,662.4
Net Investment Gain (Loss)	(4.4)	(0.1)	(22.3)	85.4
Interest and Debt Expense	47.0	44.7	141.3	134.4
Derivative, Gain (Loss) on Derivative, Net	0.9	(0.7)	(4.6)	(2.3)
Designated as Hedging Instrument | Interest Rate Swaps | Net Investment Income | Cash Flow Hedging
Derivative Instruments, Gain (Loss)
Net Investment Income	50.2	63.4	150.9	170.2
Derivative, Gain (Loss) on Derivative, Net	14.1	14.6	40.5	46.6
Designated as Hedging Instrument | Interest Rate Swaps | Net Investment Gain (Loss) | Cash Flow Hedging
Derivative Instruments, Gain (Loss)
Net Investment Gain (Loss)	0.0	0.3	0.0	2.7
Derivative, Gain (Loss) on Derivative, Net	0.0	0.2	0.0	2.0
Designated as Hedging Instrument | Interest Rate Swaps | Interest and Debt Expense | Cash Flow Hedging
Derivative Instruments, Gain (Loss)
Interest and Debt Expense	0.7	7.3	2.1	21.9
Derivative, Gain (Loss) on Derivative, Net	0.0	0.1	0.0	0.3
Designated as Hedging Instrument | Foreign Exchange Contracts | Net Investment Income | Cash Flow Hedging
Derivative Instruments, Gain (Loss)
Net Investment Income	2.7	2.9	8.3	10.1
Derivative, Gain (Loss) on Derivative, Net	(1.5)	0.3	(0.9)	1.2
Designated as Hedging Instrument | Foreign Exchange Contracts | Net Investment Income | Fair Value Hedging
Derivative Instruments, Gain (Loss)
Net Investment Income	2.9	2.5	8.7	7.2
Derivative, Gain (Loss) on Derivative, Net	1.0	0.9	5.1	3.1
Designated as Hedging Instrument | Foreign Exchange Contracts | Net Investment Gain (Loss) | Cash Flow Hedging
Derivative Instruments, Gain (Loss)
Net Investment Gain (Loss)	(0.5)	0.0	(0.5)	0.0
Derivative, Gain (Loss) on Derivative, Net	0.0	(0.1)	0.0	(0.1)
Designated as Hedging Instrument | Foreign Exchange Contracts | Net Investment Gain (Loss) | Fair Value Hedging
Derivative Instruments, Gain (Loss)
Net Investment Gain (Loss)	(29.6)	(10.4)	(62.5)	(18.8)
Derivative, Gain (Loss) on Derivative, Net	29.6	10.4	62.5	18.8
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	0.0	0.0
Derivative, Gain (Loss) on Derivative, Net	0.0	0.0	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	0.0	0.0
Derivative, Gain (Loss) on Derivative, Net	0.0	0.0	0.0	0.0
Designated as Hedging Instrument | Forwards | Net Investment Income | Cash Flow Hedging
Derivative Instruments, Gain (Loss)
Net Investment Income	0.2	0.0	0.2	0.0
Derivative, Gain (Loss) on Derivative, Net	0.0	0.0	0.0	0.0
Designated as Hedging Instrument | Forwards | Net Investment Gain (Loss) | Cash Flow Hedging
Derivative Instruments, Gain (Loss)
Net Investment Gain (Loss)	0.0	0.0	0.0	0.0
Derivative, Gain (Loss) on Derivative, Net	0.0	0.0	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	0.0	0.0
Derivative, Gain (Loss) on Derivative, Net	$ 0.0	$ 0.0	$ 0.0	$ 0.0