Fair Value of Assets and Liabilities - Fair Value Measurements (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Transfers Between Levels Amount	$ 0.0
Fair Value, Measurements, Recurring [Member]
Fair value assets measured on recurring basis
Total	51.9	$ 107.3
Fair value liabilities measured on recurring basis
Total	31.4	25.1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value assets measured on recurring basis
Total	22.0	90.8
Fair value liabilities measured on recurring basis
Total	7.5	9.4
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair value assets measured on recurring basis
Total	29.9	16.5
Fair value liabilities measured on recurring basis
Total	23.9	15.7
Short-term investments | Certificates of deposit | Fair Value, Measurements, Recurring [Member]
Fair value assets measured on recurring basis
Fair value of investment assets	14.5	81.4
Short-term investments | Certificates of deposit | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value assets measured on recurring basis
Fair value of investment assets	14.5	81.4
Short-term investments | Certificates of deposit | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair value assets measured on recurring basis
Fair value of investment assets	0.0	0.0
Securities and other investments | Interest rate swaps | Fair Value, Measurements, Recurring [Member]
Fair value assets measured on recurring basis
Derivative Asset	9.6	7.6
Securities and other investments | Interest rate swaps | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value assets measured on recurring basis
Derivative Asset	0.0	0.0
Securities and other investments | Interest rate swaps | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair value assets measured on recurring basis
Derivative Asset	9.6	7.6
Securities and other investments | Assets held in rabbi trusts [Member] | Fair Value, Measurements, Recurring [Member]
Fair value assets measured on recurring basis
Assets held in rabbi trusts	7.5	9.4
Securities and other investments | Assets held in rabbi trusts [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair value assets measured on recurring basis
Assets held in rabbi trusts	0.0	0.0
Other current assets | Foreign exchange forward contracts | Fair Value, Measurements, Recurring [Member]
Fair value assets measured on recurring basis
Derivative Asset	15.7	6.7
Other current assets | Foreign exchange forward contracts | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value assets measured on recurring basis
Derivative Asset	0.0	0.0
Other current assets | Foreign exchange forward contracts | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair value assets measured on recurring basis
Derivative Asset	15.7	6.7
Other current assets | Interest rate swaps | Fair Value, Measurements, Recurring [Member]
Fair value assets measured on recurring basis
Derivative Asset	4.6	2.2
Other current assets | Interest rate swaps | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value assets measured on recurring basis
Derivative Asset	0.0	0.0
Other current assets | Interest rate swaps | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair value assets measured on recurring basis
Derivative Asset	4.6	2.2
Other current liabilities | Foreign exchange forward contracts | Fair Value, Measurements, Recurring [Member]
Fair value liabilities measured on recurring basis
Derivative Liability	18.5	10.2
Other current liabilities | Foreign exchange forward contracts | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value liabilities measured on recurring basis
Derivative Liability	0.0	0.0
Other current liabilities | Foreign exchange forward contracts | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair value liabilities measured on recurring basis
Derivative Liability	18.5	10.2
Other current liabilities | Interest rate swaps | Fair Value, Measurements, Recurring [Member]
Fair value liabilities measured on recurring basis
Derivative Liability	5.4	5.5
Other current liabilities | Interest rate swaps | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value liabilities measured on recurring basis
Derivative Liability	0.0	0.0
Other current liabilities | Interest rate swaps | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair value liabilities measured on recurring basis
Derivative Liability	5.4	5.5
Other liabilities | Fair Value, Measurements, Recurring [Member]
Fair value liabilities measured on recurring basis
Deferred compensation	7.5	9.4
Other liabilities | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair value liabilities measured on recurring basis
Deferred compensation	0.0	0.0
Other liabilities | Assets held in rabbi trusts [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value assets measured on recurring basis
Assets held in rabbi trusts	$ 7.5	$ 9.4