Benefit Plans and Other Postretirement Benefits, Net pension expense (Details) - Pension Benefits - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Components of net pension expense:
Service cost	$ 1,900,000	$ 2,000,000.0	$ 5,600,000	$ 5,500,000
Interest cost	4,200,000	5,400,000	12,500,000	16,200,000
Expected return on plan assets	(9,300,000)	(9,200,000)	(27,800,000)	(27,800,000)
Amortization of prior service cost	500,000	400,000	1,600,000	1,300,000
Amortization of net actuarial losses	6,300,000	4,600,000	18,800,000	13,900,000
Net pension expense	3,600,000	$ 3,200,000	10,700,000	$ 9,100,000
United States
Defined Benefit Plan Disclosure
Estimated future employer contribution in fiscal year	$ 0		$ 0