EARNINGS (LOSS) PER COMMON SHARE - Computation of Basic and Diluted Net Income (Loss) Per Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Numerator:
Net income (loss) attributable to Stericycle, Inc.	$ 23.5	$ 39.0	$ 73.7	$ (46.8)
Mandatory convertible preferred stock dividend	(8.4)	(8.9)	(25.5)	(27.5)
Gain on repurchases of preferred stock	2.4	5.4	16.9	14.4
Net income (loss) attributable to Stericycle, Inc. common shareholders	$ 17.5	$ 35.5	$ 65.1	$ (59.9)
Denominator:
Denominator for basic earnings (loss) per share - weighted average shares (in shares)	86.7	85.3	85.9	85.3
Effect of dilutive securities:
Stock-based compensation awards	0.1	0.3	0.2
Denominator for diluted earnings (loss) per share - adjusted weighted average shares and after assumed exercises (in shares)	86.8	85.6	86.1	85.3
Earnings (loss) per share - Basic (in dollars per share)	$ 0.20	$ 0.42	$ 0.76	$ (0.70)
Earnings (loss) per share - Diluted (in dollars per share)	$ 0.20	$ 0.41	$ 0.76	$ (0.70)