Pension and Other Postretirement Benefits - Schedule of Fair Values of Pension Plan by Assets Category (Details) - USD ($)	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2016
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	$ 972,500,000	987,600,000	$ 885,100,000
Pension Benefits | Short-term investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	17,100,000	24,000,000
Pension Benefits | Domestic and international equities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	156,400,000	148,300,000
Pension Benefits | Commingled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	365,300,000	376,600,000
Pension Benefits | Limited partnerships
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	43,300,000	42,300,000
Pension Benefits | Government agency bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	155,100,000	154,400,000
Pension Benefits | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	226,300,000	236,200,000
Pension Benefits | Mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	1,800,000	1,800,000
Pension Benefits | Mortgage/asset backed securities and other
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	7,200,000	4,000,000
Pension Benefits | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	162,400,000	161,100,000
Pension Benefits | Level 1 | Short-term investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	2,500,000	9,400,000
Pension Benefits | Level 1 | Domestic and international equities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	156,400,000	148,300,000
Pension Benefits | Level 1 | Commingled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Pension Benefits | Level 1 | Limited partnerships
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Pension Benefits | Level 1 | Government agency bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	3,500,000	3,400,000
Pension Benefits | Level 1 | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Pension Benefits | Level 1 | Mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	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
Pension Benefits | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	399,700,000	405,800,000
Pension Benefits | Level 2 | Short-term investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	14,600,000	14,600,000
Pension Benefits | Level 2 | Domestic and international equities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Pension Benefits | Level 2 | Commingled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Pension Benefits | Level 2 | Limited partnerships
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Pension Benefits | Level 2 | Government agency bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	151,600,000	151,000,000
Pension Benefits | Level 2 | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	226,300,000	236,200,000
Pension Benefits | Level 2 | Mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Pension Benefits | Level 2 | Mortgage/asset backed securities and other
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	7,200,000	4,000,000
Pension Benefits | Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	410,400,000	420,700,000
Pension Benefits | Net Asset Value | Short-term investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	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
Pension Benefits | Net Asset Value | Commingled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	365,300,000	376,600,000
Pension Benefits | Net Asset Value | Limited partnerships
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	43,300,000	42,300,000
Pension Benefits | Net Asset Value | Government agency bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Pension Benefits | Net Asset Value | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Pension Benefits | Net Asset Value | Mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	1,800,000	1,800,000
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