Benefit Plans and Other Postretirement Benefits, Defined benefit plans (Details) - Pension Benefits - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended
	Jan. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Components of net pension expense:
Service cost		$ 1,700,000	$ 1,900,000	$ 3,500,000	$ 3,800,000
Interest cost		5,400,000	4,900,000	10,800,000	9,800,000
Expected return on plan assets		(9,200,000)	(9,600,000)	(18,500,000)	(19,300,000)
Amortization of prior service cost		400,000	600,000	800,000	1,200,000
Amortization of net actuarial losses		4,600,000	5,800,000	9,300,000	11,700,000
Net pension expense		2,900,000	$ 3,600,000	5,900,000	$ 7,200,000
United States
Defined Benefit Plan Disclosure
Estimated future employer contribution in fiscal year		$ 0		$ 0
Employer contributions	$ 81,000,000.0