Benefit Plans and Other Postretirement Benefits, Net pension expense (Details) - Pension Benefits - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Components of net pension expense:
Service cost	$ 2,000,000.0	$ 1,800,000
Interest cost	4,200,000	5,400,000
Expected return on plan assets	(9,300,000)	(9,200,000)
Amortization of prior service cost	500,000	400,000
Amortization of net actuarial losses	6,200,000	4,600,000
Net pension expense	3,600,000	$ 3,000,000.0
United States
Defined Benefit Plan Disclosure
Estimated future employer contribution in fiscal year	$ 0