Pensions and Postretirement Benefits - Schedule of Net Periodic Benefit Cost (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Pension Benefits
Defined Benefit Plan Disclosure
Service cost	$ 1,200,000	$ 1,100,000	$ 3,400,000	$ 3,400,000
Interest cost	2,500,000	3,100,000	7,900,000	9,200,000
Expected return on plan assets	(4,800,000)	(4,000,000.0)	(14,300,000)	(12,000,000.0)
Amortization of prior service cost	0	0	0	100,000
Amortization of net loss (gain)	1,400,000	1,700,000	4,000,000.0	5,000,000.0
Curtailment loss	0		300,000
Net periodic benefit cost	300,000	1,900,000	1,300,000	5,700,000
Other Benefits
Defined Benefit Plan Disclosure
Service cost	0	0	0	100,000
Interest cost	0	0	100,000	100,000
Expected return on plan assets	0	0	0	0
Amortization of prior service cost	0	100,000	0	100,000
Amortization of net loss (gain)	100,000	0	(1,000,000.0)	0
Curtailment loss	0		0
Net periodic benefit cost	100,000	$ 100,000	(900,000)	$ 300,000
U.S.
Defined Benefit Plan Disclosure
Contributions by employer			0
Expected future contributions	$ 4,000,000.0		$ 4,000,000.0