Pension and Other Postretirement Benefits - Schedule of Fair Values of Other Postretirement Benefit Plans by Asset Category (Details) - Other Benefits - USD ($) $ in Millions	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2023
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	$ 143.3	$ 136.3	$ 120.4
Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	0.6	6.6
Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	0.0	0.0
Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	142.7	129.7
Commingled trust funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	142.7	129.7
Commingled trust funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	0.0	0.0
Commingled trust funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	0.0	0.0
Commingled trust funds | Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	142.7	129.7
Short-term investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	0.6	6.6
Short-term investments | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	0.6	6.6
Short-term investments | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	0.0	0.0
Short-term investments | Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	$ 0.0	$ 0.0