Derivatives and Hedging (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
	Jan. 18, 2022	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Jun. 30, 2022	Dec. 31, 2021	Jun. 30, 2021	Dec. 31, 2020	Jul. 31, 2016	Jul. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Other comprehensive income		$ (55.1)	$ 1,084.0	$ (55.1)	$ 1,084.0	$ (71.0)	$ (17.6)	$ 863.9	$ 384.4
Amortization	$ 1.3
Interest expense		$ 4.6	6.2	$ 15.9	18.7
Senior Notes, 5.125%, due 2031 | Senior notes
Derivative Instruments, Gain (Loss) [Line Items]
Debt repayments	$ 125.0
Stated interest rate	5.125%	5.125%		5.125%
Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) reclassified from AOCI to interest expense		$ 0.8	0.8	$ 3.8	2.4
Loss amount reclassified within twelve months				3.4
Valuation and amortization of derivative securities
Derivative Instruments, Gain (Loss) [Line Items]
Other comprehensive income		(12.8)	(16.2)	(12.8)	(16.2)	(13.4)	(15.6)	(16.8)	(18.0)
Accumulated other comprehensive income (loss)
Derivative Instruments, Gain (Loss) [Line Items]
Other comprehensive income		$ (13.6)	$ (11.5)	(13.6)	$ (11.5)	$ (11.7)	$ (10.8)	$ (11.2)	$ (13.6)
Accumulated other comprehensive income (loss) | Reclassification out of Accumulated Other Comprehensive Income
Derivative Instruments, Gain (Loss) [Line Items]
Interest expense				$ 3.8
Treasury Lock | Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount											$ 300.0
Fair value of derivative										$ (34.4)