GOODWILL AND OTHER INTANGIBLE ASSETS - Carrying Values of Other Intangible Assets (Detail) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017	Dec. 31, 2016
Intangible Assets By Major Class [Line Items]
Gross Carrying Amount	$ 2,144.7	$ 2,184.0
Accumulated Amortization	446.0	392.5
Net Value	1,698.7	1,791.5	$ 1,862.0
Operating permits
Intangible Assets By Major Class [Line Items]
Carrying Amount, Indefinite Lived Intangible Assets	216.3	222.3
Tradenames
Intangible Assets By Major Class [Line Items]
Carrying Amount, Indefinite Lived Intangible Assets	314.7	317.4
Customer relationships
Intangible Assets By Major Class [Line Items]
Gross Carrying Amount	1,590.0	1,613.4
Accumulated Amortization	435.7	381.4
Net Value	1,154.3	1,232.0
Covenants not-to-compete
Intangible Assets By Major Class [Line Items]
Gross Carrying Amount	7.7	7.9
Accumulated Amortization	6.3	5.9
Net Value	1.4	2.0
Tradenames
Intangible Assets By Major Class [Line Items]
Gross Carrying Amount	4.0	6.0
Accumulated Amortization	1.1	1.8
Net Value	2.9	4.2
Other
Intangible Assets By Major Class [Line Items]
Gross Carrying Amount	12.0	17.0
Accumulated Amortization	2.9	3.4
Net Value	$ 9.1	$ 13.6