Pension and Other Postretirement Benefits - Schedule of Fair Values of Other Postretirement Benefit Plans by Asset Category (Details) - Other Postretirement Plans - USD ($) $ in Millions	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2014
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 115.6	$ 111.6	$ 106.5
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	115.6	111.6
Commingled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	64.0	63.1
Commingled funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Commingled funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	64.0	63.1
Short-term investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	23.8	21.6
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	23.8	21.6
Government agency bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	16.1	16.0
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	16.1	16.0
Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	9.9	8.6
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	9.9	8.6
Mortgage/ asset backed securities and other
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	1.8	2.3
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	$ 1.8	$ 2.3