(LOSS) EARNINGS PER COMMON SHARE - Computation of Basic and Diluted (Loss) Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Numerator:
Net (loss) income attributable to Stericycle, Inc.	$ (59.2)	$ 23.5	$ (127.5)	$ 73.7
Mandatory convertible preferred stock dividend		(8.4)		(25.5)
Gain on repurchases of preferred stock		2.4		16.9
Net (loss) income attributable to Stericycle, Inc. common shareholders	$ (59.2)	$ 17.5	$ (127.5)	$ 65.1
Denominator:
Denominator for basic (loss) earnings per share - weighted average shares (in shares)	91.1	86.7	91.0	85.9
Effect of dilutive securities:
Stock-based compensation awards		0.2		0.2
Denominator for diluted (loss) earnings per share - adjusted weighted average shares and after assumed exercises	91.1	86.8	91.0	86.1
(Loss) earnings per share - Basic (in dollars per share)	$ (0.65)	$ 0.20	$ (1.40)	$ 0.76
(Loss) earnings per share - Diluted (in dollars per share)	$ (0.65)	$ 0.20	$ (1.40)	$ 0.76