Derivative Financial Instruments Location of Gains and Losses Designated as Hedging Instruments, Consolidated Statements of Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Derivative Instruments, Gain (Loss)
Net Investment Income	$ 559.0	$ 563.5	$ 1,086.2	$ 1,112.2
Net Investment Gain (Loss)	(4.1)	0.9	(17.9)	85.5
Interest and Debt Expense	47.4	45.3	94.3	89.7
Derivative, Gain (Loss) on Derivative, Net	(3.7)	0.1	(5.5)	(1.6)
Designated as Hedging Instrument | Interest Rate Swaps | Net Investment Income | Cash Flow Hedging
Derivative Instruments, Gain (Loss)
Net Investment Income	50.3	54.8	100.7	106.8
Derivative, Gain (Loss) on Derivative, Net	13.0	16.5	26.4	32.0
Designated as Hedging Instrument | Interest Rate Swaps | Net Investment Gain (Loss) | Cash Flow Hedging
Derivative Instruments, Gain (Loss)
Net Investment Gain (Loss)	0.0	0.0	0.0	2.4
Derivative, Gain (Loss) on Derivative, Net	0.0	0.0	0.0	1.8
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	1.4	14.6
Derivative, Gain (Loss) on Derivative, Net	0.0	0.1	0.0	0.2
Designated as Hedging Instrument | Foreign Exchange Contracts | Net Investment Income | Cash Flow Hedging
Derivative Instruments, Gain (Loss)
Net Investment Income	2.8	4.1	5.6	7.2
Derivative, Gain (Loss) on Derivative, Net	0.4	0.6	0.6	0.9
Designated as Hedging Instrument | Foreign Exchange Contracts | Net Investment Income | Fair Value Hedging
Derivative Instruments, Gain (Loss)
Net Investment Income	3.1	2.4	5.8	4.7
Derivative, Gain (Loss) on Derivative, Net	2.7	1.2	4.1	2.2
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	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 | Net Investment Gain (Loss) | Fair Value Hedging
Derivative Instruments, Gain (Loss)
Net Investment Gain (Loss)	(27.6)	1.1	(32.9)	(8.4)
Derivative, Gain (Loss) on Derivative, Net	27.6	(1.1)	32.9	8.4
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