Retirement Benefits - Components of Pension and Other Benefit Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Benefits
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 5.9	$ 12.9	$ 17.7
Interest cost	37.2	41.9	40.5
Expected return on plan assets	(34.1)	(44.3)	(53.2)
Amortization of prior service cost (credit)	0.1	0.1	0.2
Amortization of actuarial losses (gains)	11.4	13.9	12.1
Curtailment and settlement losses	0.4	0.2	0.0
Net periodic benefit cost	20.9	24.7	17.3
Other Comprehensive (Income) Loss, Defined Benefit Plan, before Reclassification Adjustment, after Tax [Abstract]
Current year net actuarial loss	4.2	72.0	37.0
Current year prior service credit	0.3	0.0	0.0
Amortization of prior service (cost) credit	(0.1)	(0.1)	(0.2)
Amortization of net actuarial (losses) gains	(11.4)	(13.9)	(12.1)
Currency impact	3.5	(4.0)	(0.1)
Other adjustments	(0.4)	(0.2)	0.0
Total recognized in other comprehensive loss	(3.9)	53.8	24.6
Defined Benefit Plan, Amount Recognized in Net Periodic Benefit Cost (Credit) and Other Comprehensive (Income) Loss, before Tax	17.0	78.5	41.9
Defined Benefit Plan, Expected Amortization, Next Fiscal Year [Abstract]
Amortization of prior service cost (credit)	0.1
Amortization of net loss	10.9
TOTAL EXPECTED TO BE RECOGNIZED THROUGH INCOME DURING NEXT FISCAL YEAR	11.0
Other Benefits
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	0.1	0.0	0.1
Interest cost	1.0	1.2	1.0
Expected return on plan assets		0.0	0.0
Amortization of prior service cost (credit)	(1.0)	(1.0)	(1.0)
Amortization of actuarial losses (gains)	0.0	0.0	(0.1)
Curtailment and settlement losses	0.0	0.0	0.0
Net periodic benefit cost	0.1	0.2	0.0
Other Comprehensive (Income) Loss, Defined Benefit Plan, before Reclassification Adjustment, after Tax [Abstract]
Current year net actuarial loss	1.4	0.2	0.5
Current year prior service credit		0.0	0.0
Amortization of prior service (cost) credit	1.0	1.0	1.0
Amortization of net actuarial (losses) gains	0.0	0.0	0.1
Currency impact	0.0	0.0	0.0
Other adjustments	0.0	0.0	0.0
Total recognized in other comprehensive loss	2.4	1.2	1.6
Defined Benefit Plan, Amount Recognized in Net Periodic Benefit Cost (Credit) and Other Comprehensive (Income) Loss, before Tax	2.5	$ 1.4	$ 1.6
Defined Benefit Plan, Expected Amortization, Next Fiscal Year [Abstract]
Amortization of prior service cost (credit)	(1.0)
Amortization of net loss	0.2
TOTAL EXPECTED TO BE RECOGNIZED THROUGH INCOME DURING NEXT FISCAL YEAR	$ (0.8)