Financial Instruments - Derivative Hedging Activities (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Interest expense	$ (98.5)	$ (96.5)	$ (198.9)	$ (191.3)
Realized gain reclassified into earnings	(0.2)		(0.3)
Interest Expense | Interest Rate Swap
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Realized gain reclassified into earnings	0.1		0.2
Interest Expense | Interest Rate Swap Locks
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Realized gain reclassified into earnings	$ 0.3		$ 0.4
Fair Value Hedging | Interest Expense | Interest Rate Swap
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain (loss) reclassified from AOCI into earnings		0.5		1.4
Fair Value Hedging | Other Income | Interest Rate Swap
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Net periodic earnings		0.2		0.2
Net periodic earnings		(0.2)		(0.2)
Cash Flow Hedging | Interest Expense | Interest Rate Swap Locks
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain (loss) reclassified from AOCI into earnings		$ (0.3)		$ (0.8)