Pension and Other Postretirement Benefits - Schedule of Fair Values of Pension Plan by Assets Category (Details) - USD ($) $ in Millions	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 964.7	972.5	$ 987.6
Pension Benefits | Short-term investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	14.9	17.1
Pension Benefits | Domestic and international equities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	132.6	156.4
Pension Benefits | Commingled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	371.4	365.3
Pension Benefits | Limited partnerships
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	45.4	43.3
Pension Benefits | Government agency bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	176.8	155.1
Pension Benefits | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	220.2	226.3
Pension Benefits | Mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	1.9	1.8
Pension Benefits | Mortgage/asset backed securities and other
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	1.5	7.2
Pension Benefits | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	144.7	162.4
Pension Benefits | Level 1 | Short-term investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	5.4	2.5
Pension Benefits | Level 1 | Domestic and international equities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	132.6	156.4
Pension Benefits | Level 1 | Commingled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Pension Benefits | Level 1 | Limited partnerships
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Pension Benefits | Level 1 | Government agency bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	4.8	3.5
Pension Benefits | Level 1 | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Pension Benefits | Level 1 | Mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	1.9	0.0
Pension Benefits | Level 1 | Mortgage/asset backed securities and other
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Pension Benefits | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	403.2	399.7
Pension Benefits | Level 2 | Short-term investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	9.5	14.6
Pension Benefits | Level 2 | Domestic and international equities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Pension Benefits | Level 2 | Commingled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Pension Benefits | Level 2 | Limited partnerships
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Pension Benefits | Level 2 | Government agency bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	172.0	151.6
Pension Benefits | Level 2 | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	220.2	226.3
Pension Benefits | Level 2 | Mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Pension Benefits | Level 2 | Mortgage/asset backed securities and other
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	1.5	7.2
Pension Benefits | Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	416.8	410.4
Pension Benefits | Net Asset Value | Short-term investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Pension Benefits | Net Asset Value | Domestic and international equities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Pension Benefits | Net Asset Value | Commingled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	371.4	365.3
Pension Benefits | Net Asset Value | Limited partnerships
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	45.4	43.3
Pension Benefits | Net Asset Value | Government agency bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Pension Benefits | Net Asset Value | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Pension Benefits | Net Asset Value | Mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	1.8
Pension Benefits | Net Asset Value | Mortgage/asset backed securities and other
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 0.0	$ 0.0