Pension and Other Postretirement Benefits - Schedule of Components of the Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Mar. 31, 2017	Sep. 30, 2016	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Pension Plans
Pension and Other Postretirement Benefit Disclosures
Service cost	$ 2.2		$ 7.8	$ 18.1	$ 23.4
Interest cost	12.4		14.4	37.8	43.2
Expected return on plan assets	(16.6)		(16.4)	(48.4)	(49.3)
Amortization of net loss	9.5		6.8	28.3	20.5
Amortization of prior service cost (benefit)	0.5		0.1	1.3	0.3
Curtailment charge		$ 0.5		0.5	0.0
Net periodic benefit costs	8.0		12.7	37.6	38.1
Other Postretirement Plans
Pension and Other Postretirement Benefit Disclosures
Service cost	0.9		0.8	2.8	2.5
Interest cost	2.3		2.5	6.9	7.7
Expected return on plan assets	(1.7)		(1.7)	(5.1)	(5.2)
Amortization of net loss	0.8		0.7	2.4	2.0
Amortization of prior service cost (benefit)	(1.6)		(1.6)	(4.9)	(4.8)
Curtailment charge				0.0	0.0
Net periodic benefit costs	$ 0.7		$ 0.7	$ 2.1	$ 2.2