Derivatives and Hedging (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018	Jul. 31, 2016	Jul. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Other comprehensive income	$ 119.3	$ 114.5	$ 8.4	$ 134.2
Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Loss amount reclassified within twelve months	3.2
Valuation and amortization of derivative securities
Derivative Instruments, Gain (Loss) [Line Items]
Other comprehensive income	(19.8)	(20.3)	(22.1)	(22.7)
Accumulated other comprehensive income (loss)
Derivative Instruments, Gain (Loss) [Line Items]
Other comprehensive income	(19.1)	$ (17.5)	$ (19.8)	$ (20.9)
Accumulated other comprehensive income (loss) | Reclassification out of Accumulated Other Comprehensive Income
Derivative Instruments, Gain (Loss) [Line Items]
Interest expense	$ 0.7
Treasury Lock | Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount						$ 300.0
Fair value of derivative					$ 34.4