Accumulated Other Comprehensive Loss - Schedule of Reclassifications of Recognized Transactions out of AOCI (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income (loss), net	$ 2.7	$ (9.8)
Net income	50.7	35.7
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income	(0.2)	(5.9)
Reclassification out of Accumulated Other Comprehensive Income | Unrealized holding gains (losses) available-for-sale debt securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income (loss), net	0.0	(5.6)
Reclassification out of Accumulated Other Comprehensive Income | Amortization of actuarial loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income (loss), net	$ (0.2)	$ (0.3)