Fair Value Measurements - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-recurring fair value adjustments	$ 0.0	$ 0.0	$ 0.0	$ 0.0
Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes and other borrowings	3,331.8		3,331.8		$ 3,033.6
Level 2 | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes and other borrowings	3,363.3		3,363.3		3,146.5
Foreign corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of foreign corporate debt securities	43.5		43.5		56.2
Fair value of foreign corporate debt securities	43.5		43.5		56.2
Foreign corporate debt securities | Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of foreign corporate debt securities	43.5		43.5		56.2
Foreign corporate debt securities | Level 2 | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of foreign corporate debt securities	$ 43.5		$ 43.5		$ 56.2