Pension and Postretirement Benefits - Components of Net Periodic (Income) Cost Associated with Pension Plans and Postretirement Benefit Obligations (Details) - USD ($)		1 Months Ended	3 Months Ended		9 Months Ended
	Feb. 08, 2019	Feb. 07, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Amortization of Prior Service Cost (Credit)	$ 0
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 300,000	$ 400,000	$ 400,000	$ 1,300,000	$ 1,000,000.0
Interest cost		6,800,000	10,600,000	13,200,000	31,500,000	33,600,000
Expected return on plan assets		(10,600,000)	(21,800,000)	(23,200,000)	(65,500,000)	(59,400,000)
Amortization of Prior Service Cost (Credit)		0	0	0	0	0
Recognized actuarial loss (gain)		4,000,000.0	0	0	0	0
Net periodic cost (income)		500,000	(10,800,000)	(9,600,000)	(32,700,000)	(24,800,000)
Postretirement Benefit Obligations
Defined Benefit Plan Disclosure [Line Items]
Service cost		0	0	0	0	0
Interest cost		0	0	0	0	100,000
Expected return on plan assets		0	0	0	0	0
Amortization of Prior Service Cost (Credit)		(100,000)	(100,000)	0	(300,000)	0
Recognized actuarial loss (gain)		(100,000)	0	0	0	0
Net periodic cost (income)		$ (200,000)	$ (100,000)	$ 0	$ (300,000)	$ 100,000