POSTRETIREMENT BENEFIT PLANS - Net Periodic Benefit Cost of Pension Plans and Other Employee Related Benefit Plans (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 0.6	$ 0.8	$ 1.2	$ 1.6
Interest cost		3.9	4.2	7.8	8.3
Expected return on plan assets(a)	[1]	(3.5)	(3.8)	(7.0)	(7.7)
Amortization of prior service cost (benefit)		(1.1)	(1.2)	(2.2)	(2.4)
Amortization of net actuarial loss		2.6	2.8	5.2	5.6
Total net periodic benefit cost		2.5	2.8	5.0	5.4
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		0.4	0.6	0.8	1.2
Interest cost		2.8	3.0	5.6	6.0
Expected return on plan assets(a)		(3.4)	(3.7)	(6.8)	(7.5)
Amortization of prior service cost (benefit)		0.2	0.3	0.4	0.5
Amortization of net actuarial loss		1.5	1.8	3.0	3.5
Total net periodic benefit cost		1.5	2.0	3.0	3.7
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		0.2	0.2	0.4	0.4
Interest cost		1.1	1.2	2.2	2.3
Expected return on plan assets(a)		(0.1)	(0.1)	(0.2)	(0.2)
Amortization of prior service cost (benefit)		(1.3)	(1.5)	(2.6)	(2.9)
Amortization of net actuarial loss		1.1	1.0	2.2	2.1
Total net periodic benefit cost		$ 1.0	$ 0.8	$ 2.0	$ 1.7

[1] (a) Includes plan administrative expenses of $0.9 and $0.8, and $1.8 and $1.6 for the three and six months ended June 30, 2018 and 2017, respectively. The prior year plan administrative expenses have been reclassified from the service cost component line to conform to the current year presentation.