Retirement Benefits - Status of Plans (Details) - USD ($) $ in Millions	12 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Actuarial gains	$ (0.4)	$ (3.3)	$ (2.6)
Plan assets at the beginning of the period	507.4
Contributions	1.3	2.9	4.9
Plan assets at end of period	480.2	507.4
Net amount on Consolidated Balance Sheets consists of:
Current liabilities	(3.3)	(4.0)
Long-term liabilities	(158.0)	(163.2)
Pension Benefits
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Benefit obligation at beginning of period	(652.5)	(659.3)
Service cost	(0.5)	(1.0)	(1.8)
Interest cost	(23.6)	(24.3)	(25.6)
Actuarial gains	1.7	7.1
Benefits paid	40.7	40.8
Plan participant contributions	0.0	(0.1)
Acquisitions	0.0	(6.3)
Curtailments	0.0	0.3
Settlements	3.2	0.0
Translation and other adjustments	7.2	(9.7)
Benefit obligation at end of period	(623.8)	(652.5)	(659.3)
Plan assets at the beginning of the period	507.4	513.0
Actual return on plan assets	15.8	23.6
Contributions	4.0	5.5
Benefits paid	(40.7)	(40.8)
Acquisition	0.0	2.3
Settlements	(3.4)	0.0
Translation adjustment	(2.9)	3.8
Plan assets at end of period	480.2	507.4	513.0
Funded status of plans	(143.6)	(145.1)
Net amount on Consolidated Balance Sheets consists of:
Non-current assets	0.8	0.6
Current liabilities	(1.7)	(1.9)
Long-term liabilities	(142.7)	(143.8)
Total net funded status	(143.6)	(145.1)
Postretirement Benefits
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Benefit obligation at beginning of period	(21.5)	(25.7)
Service cost	0.0	0.0	(0.1)
Interest cost	(0.8)	(1.0)	(1.1)
Actuarial gains	2.5	2.8
Benefits paid	1.9	3.0
Plan participant contributions	(0.5)	(0.6)
Acquisitions	0.0	0.0
Curtailments	0.0	0.0
Settlements	0.0	0.0
Translation and other adjustments	1.5	0.0
Benefit obligation at end of period	(16.9)	(21.5)	(25.7)
Plan assets at the beginning of the period	0.0	0.0
Actual return on plan assets	0.0	0.0
Contributions	2.5	3.0
Benefits paid	(2.5)	(3.0)
Acquisition	0.0	0.0
Settlements	0.0	0.0
Translation adjustment	0.0	0.0
Plan assets at end of period	0.0	0.0	$ 0.0
Funded status of plans	(16.9)	(21.5)
Net amount on Consolidated Balance Sheets consists of:
Non-current assets	0.0	0.0
Current liabilities	(1.6)	(2.1)
Long-term liabilities	(15.3)	(19.4)
Total net funded status	$ (16.9)	$ (21.5)

Amount of increase (decrease) in plan assets of defined benefit plan from actual return (loss) determined by change in fair value of plan assets adjusted for contributions, benefit payments, and other expenses.

Name:	us-gaap_DefinedBenefitPlanActualReturnOnPlanAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of gain (loss) from change in actuarial assumptions which (increases) decreases benefit obligation of defined benefit plan. Assumptions include, but are not limited to, interest, mortality, employee turnover, salary, and temporary deviation from substantive plan.