EARNINGS PER COMMON SHARE - Computation of Basic and Diluted Net Income Per Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Numerator:
Net income attributable to Stericycle, Inc.	$ 22.5	$ 58.2
Mandatory convertible preferred stock dividend	(8.8)	(9.4)
Gain on repurchase of preferred stock	7.3	4.6
Net income attributable to Stericycle, Inc. common shareholders	$ 21.0	$ 53.4
Denominator:
Denominator for basic earnings per share-weighted average shares (in shares)	85.5	85.2
Effect of dilutive securities:
Stock-based compensation awards	0.3	0.4
Mandatory convertible preferred stock (in shares)	0.0	0.0
Denominator for diluted earnings per share-adjusted weighted average shares and after assumed exercises (in shares)	85.8	85.6
Earnings per share - Basic (in dollars per share)	$ 0.25	$ 0.63
Earnings per share - Diluted (in dollars per share)	$ 0.25	$ 0.62