POSTRETIREMENT BENEFIT PLANS - Net Periodic Benefit Cost of Pension Plans and Other Employee Related Benefit Plans (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0.6	$ 0.6	$ 1.6	$ 1.6
Interest cost	3.0	4.1	9.0	12.4
Expected return on plan assets	(2.2)	(3.9)	(6.5)	(11.1)
Amortization of prior service (benefit) cost	(1.3)	(1.1)	(3.8)	(3.3)
Amortization of net actuarial loss	2.4	1.9	7.3	5.6
Total net periodic benefit cost	2.5	1.6	7.6	5.2
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.4	0.4	1.0	1.1
Interest cost	2.2	3.1	6.8	9.4
Expected return on plan assets	(2.2)	(3.8)	(6.5)	(11.0)
Amortization of prior service (benefit) cost	0.0	0.2	0.0	0.6
Amortization of net actuarial loss	1.8	1.3	5.3	3.9
Total net periodic benefit cost	2.2	1.2	6.6	4.0
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.2	0.2	0.6	0.5
Interest cost	0.8	1.0	2.2	3.0
Expected return on plan assets	0.0	(0.1)	0.0	(0.1)
Amortization of prior service (benefit) cost	(1.3)	(1.3)	(3.8)	(3.9)
Amortization of net actuarial loss	0.6	0.6	2.0	1.7
Total net periodic benefit cost	$ 0.3	$ 0.4	$ 1.0	$ 1.2