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, 2017	Jun. 30, 2016	Jun. 30, 2015
Defined Benefit Plan Disclosure [Line Items]
Net Asset Value	$ 73.0	$ 64.0
Fair value of pension plan assets	117.0	115.6	$ 111.6
Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	44.0	51.6
Commingled funds
Defined Benefit Plan Disclosure [Line Items]
Net Asset Value	73.0	64.0
Short-term investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	22.4	23.8
Short-term investments | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Short-term investments | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	22.4	23.8
Government agency bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	12.2	16.1
Government agency bonds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Government agency bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	12.2	16.1
Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	8.2	9.9
Corporate bonds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Corporate bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	8.2	9.9
Mortgage/asset backed securities and other
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	1.2	1.8
Mortgage/asset backed securities and other | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Mortgage/asset backed securities and other | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 1.2	$ 1.8