Pension and Other Postretirement Benefits - Schedule of Fair Values of Other Postretirement Benefit Plans by Asset Category (Details) - USD ($) $ in Millions	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2022
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	$ 136.3	120.4	$ 114.7
Other Benefits | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	6.6	10.3
Other Benefits | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	0.0	0.0
Other Benefits | Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	129.7	110.1
Other Benefits | Commingled trust funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	129.7	110.1
Other Benefits | Commingled trust funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	0.0	0.0
Other Benefits | Commingled trust funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	0.0	0.0
Other Benefits | Commingled trust funds | Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	129.7	110.1
Other Benefits | Short-term investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	6.6	10.3
Other Benefits | Short-term investments | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	6.6	10.3
Other Benefits | Short-term investments | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	0.0	0.0
Other Benefits | 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