Financial Instruments - Changes in AOCI Related to Cash Flow Hedges (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Change in AOCI [Roll Forward]
Balance, beginning			$ (85.7)
Other comprehensive income (loss)	$ (34.0)	$ 19.6	(10.7)	$ 31.3
Balance, ending	(102.9)		(102.9)
Accumulated Foreign Currency Adjustment
Change in AOCI [Roll Forward]
Balance, beginning	(3.8)	0.8	(4.0)	0.9
Other comprehensive income before reclassifications	0.0	(0.3)	0.3	(0.2)
Amounts reclassified from accumulated other comprehensive loss	0.3	(0.3)	0.2	(0.5)
Other comprehensive income (loss)	0.3	(0.6)	0.5	(0.7)
Balance, ending	$ (3.5)	$ 0.2	$ (3.5)	$ 0.2