Benefit Plans and Other Postretirement Benefits, Net pension expense (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
	Jan. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Pension Benefits
Defined Benefit Plan Disclosure
Estimated future employer contribution in fiscal year		$ 90.0		$ 90.0
Components of net pension expense:
Service cost		1.8	$ 2.5	5.6	$ 7.3
Interest cost		4.9	5.0	14.7	14.9
Expected return on plan assets		(9.6)	(7.8)	(28.9)	(23.2)
Amortization of prior service cost		0.6	0.7	1.8	2.1
Amortization of net actuarial losses		5.8	5.8	17.5	17.2
Net pension expense		3.5	6.2	10.7	18.3
Pension Benefits | United States
Defined Benefit Plan Disclosure
Plan contributions by employer	$ 81.0
Other Postretirement Benefits
Components of net pension expense:
Interest cost		0.1	0.1	0.3	0.3
Amortization of net actuarial losses		0.1	0.2	0.3	0.5
Net pension expense		$ 0.2	$ 0.3	$ 0.6	$ 0.8