Accumulated Other Comprehensive Income (Loss) - Reclassification out of AOCI (Details) - USD ($) $ in Millions	12 Months Ended
	May 31, 2024	May 31, 2023	May 31, 2022
Pension Plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from Accumulated other comprehensive income (loss)	$ 1.3	$ 0.5	$ 0.9
Postretirement Benefits
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from Accumulated other comprehensive income (loss)	(0.6)	(0.6)	(0.6)
Net amortization and deferrals | Pension Plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of net actuarial loss (gain)		0.0	0.0
Net amortization and deferrals | Postretirement Benefits
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of net actuarial loss (gain)		(0.8)	(0.8)
Recognized net actuarial loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from Accumulated other comprehensive income (loss)	1.3	0.5
Amortization of prior service (credit) cost	(0.6)	(0.6)
Recognized net actuarial loss | Pension Plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of net actuarial loss (gain)		0.5	0.9
Amounts reclassified from Accumulated other comprehensive income (loss)	1.3	0.5
Amortization of prior service (credit) cost	0.0	0.0
Recognized net actuarial loss | Postretirement Benefits
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of net actuarial loss (gain)		0.0	0.0
Amounts reclassified from Accumulated other comprehensive income (loss)	0.0	0.0
Amortization of prior service (credit) cost	(0.6)	(0.6)
Accumulated Defined Benefit Plans Adjustment | Pension Plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Tax (benefit) expense	0.0	0.0	0.0
Accumulated Defined Benefit Plans Adjustment | Postretirement Benefits
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Tax (benefit) expense	0.2	$ 0.2	$ 0.2
Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Including Portion Attributable to Noncontrolling Interest | Pension Plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of net actuarial loss (gain)	1.3
Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Including Portion Attributable to Noncontrolling Interest | Postretirement Benefits
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of net actuarial loss (gain)	0.0
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Including Portion Attributable to Noncontrolling Interest | Pension Plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of net actuarial loss (gain)	0.0
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Including Portion Attributable to Noncontrolling Interest | Postretirement Benefits
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of net actuarial loss (gain)	$ (0.8)