Pension and Other Postretirement Benefits - Schedule of Fair Values of Other Postretirement Benefit Plans by Asset Category (Details) - USD ($) $ in Millions	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 117.9	117.0	$ 115.6
Other Benefits | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Other Benefits | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	37.6	44.0
Other Benefits | Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	80.3	73.0
Other Benefits | Commingled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	80.3	73.0
Other Benefits | Commingled funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Other Benefits | Commingled funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Other Benefits | Commingled funds | Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	80.3	73.0
Other Benefits | Short-term investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	23.0	22.4
Other Benefits | Short-term investments | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Other Benefits | Short-term investments | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	23.0	22.4
Other Benefits | Short-term investments | Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Other Benefits | Government agency bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	8.7	12.2
Other Benefits | Government agency bonds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Other Benefits | Government agency bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	8.7	12.2
Other Benefits | Government agency bonds | Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Other Benefits | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	5.4	8.2
Other Benefits | Corporate bonds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Other Benefits | Corporate bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	5.4	8.2
Other Benefits | Corporate bonds | Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Other Benefits | Mortgage/asset backed securities and other
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.5	1.2
Other Benefits | Mortgage/asset backed securities and other | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Other Benefits | Mortgage/asset backed securities and other | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.5	1.2
Other Benefits | Mortgage/asset backed securities and other | Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 0.0	$ 0.0