Benefit Plans and Other Postretirement Benefits, Net pension expense (Details) - Pension Benefits - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Components of net pension expense:
Service cost	$ 1.9	$ 2.0
Interest cost	2.8	4.2
Expected return on plan assets	(7.8)	(9.3)
Amortization of prior service cost	0.5	0.5
Amortization of net actuarial losses	6.2	6.2
Net pension expense	3.6	$ 3.6
United States
Defined Benefit Plan Disclosure
Estimated future employer contribution in fiscal year	$ 0.0
Weighted average assumptions used to determine net periodic benefit cost/expense:
Expected long-term return on assets (as a percent)	6.00%