Pension and Other Postretirement Benefits - Schedule of Components of the Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015
Pension Plans
Pension and Other Postretirement Benefit Disclosures
Service cost	$ 7.7		$ 7.8	$ 16.0	$ 15.6
Interest cost	12.4		14.4	25.3	28.8
Expected return on plan assets	(16.6)		(16.4)	(31.9)	(32.9)
Amortization of net loss	9.5		6.8	18.9	13.7
Amortization of prior service cost (benefit)	0.5		0.1	0.8	0.2
Curtailment charge		$ 0.5		0.5	0.0
Net periodic benefit costs	13.5		12.7	29.6	25.4
Other Postretirement Plans
Pension and Other Postretirement Benefit Disclosures
Service cost	0.9		0.8	1.8	1.7
Interest cost	2.3		2.5	4.6	5.2
Expected return on plan assets	(1.7)		(1.7)	(3.4)	(3.5)
Amortization of net loss	0.8		0.7	1.6	1.4
Amortization of prior service cost (benefit)	(1.6)		(1.6)	(3.2)	(3.3)
Curtailment charge				0.0	0.0
Net periodic benefit costs	$ 0.7		$ 0.7	$ 1.4	$ 1.5