Retirement Benefits - Status of Plans (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Actuarial (losses) gains	$ 35.8	$ 36.6	$ (0.4)	$ (3.3)
Plan assets at the beginning of the period		480.2
Contributions		0.3	1.3	2.9
Plan assets at end of period	446.9	446.9	480.2
Net amount on Consolidated Balance Sheets consists of:
Current liabilities	(3.2)	(3.2)	(3.3)
Long-term liabilities	(189.6)	(189.6)	(158.0)
Pension Benefits
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Benefit obligation at beginning of period		(623.8)	(652.5)
Service cost		(0.5)	(0.5)	(1.0)
Interest cost		(21.9)	(23.6)	(24.3)
Actuarial (losses) gains		(33.0)	1.7
Benefits paid		54.0	40.7
Plan participant contributions		0.0	0.0
Settlements		0.0	3.2
Translation and other adjustments		2.0	7.2
Benefit obligation at end of period	(623.2)	(623.2)	(623.8)	(652.5)
Plan assets at the beginning of the period		480.2	507.4
Actual return on plan assets		15.0	15.8
Contributions		6.6	4.0
Benefits paid		(54.0)	(40.7)
Settlements		0.0	(3.4)
Translation adjustment		(0.9)	(2.9)
Plan assets at end of period	446.9	446.9	480.2	507.4
Funded status of plans	(176.3)	(176.3)	(143.6)
Net amount on Consolidated Balance Sheets consists of:
Non-current assets	0.4	0.4	0.8
Current liabilities	(1.6)	(1.6)	(1.7)
Long-term liabilities	(175.1)	(175.1)	(142.7)
Total net funded status	(176.3)	(176.3)	(143.6)
Postretirement Benefits
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Benefit obligation at beginning of period		(16.9)	(21.5)
Service cost		0.0	0.0	0.0
Interest cost		(0.7)	(0.8)	(1.0)
Actuarial (losses) gains		(0.6)	2.5
Benefits paid		2.4	1.9
Plan participant contributions		(0.3)	(0.5)
Settlements		0.0	0.0
Translation and other adjustments		0.0	1.5
Benefit obligation at end of period	(16.1)	(16.1)	(16.9)	(21.5)
Plan assets at the beginning of the period		0.0	0.0
Actual return on plan assets		0.0	0.0
Contributions		2.4	2.5
Benefits paid		(2.4)	(2.5)
Settlements		0.0	0.0
Translation adjustment		0.0	0.0
Plan assets at end of period	0.0	0.0	0.0	$ 0.0
Funded status of plans	(16.1)	(16.1)	(16.9)
Net amount on Consolidated Balance Sheets consists of:
Non-current assets	0.0	0.0	0.0
Current liabilities	(1.6)	(1.6)	(1.6)
Long-term liabilities	(14.5)	(14.5)	(15.3)
Total net funded status	$ (16.1)	$ (16.1)	$ (16.9)