LOSS PER COMMON SHARE - Computation of Basic and Diluted (Loss) Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions		3 Months Ended								12 Months Ended
	Sep. 14, 2018	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Numerator:
Net loss attributable to Stericycle, Inc.										$ (57.3)	$ (346.8)	$ (244.7)
Mandatory convertible preferred stock dividend										0.0	0.0	(25.5)
Gain on repurchase of preferred stock										0.0	0.0	16.9
Net loss attributable to Stericycle, Inc. common shareholders		$ 48.5	$ (81.2)	$ (4.5)	$ (20.1)	$ (219.3)	$ (59.2)	$ (30.5)	$ (37.8)	$ (57.3)	$ (346.8)	$ (253.3)
Denominator:
Denominator for basic loss per share-weighted average shares (in shares)										91,500	91,000	87,100
Effect of dilutive securities:
Stock-based compensation awards (in shares)										0	0	0
Mandatory convertible preferred stock (in shares)										0	0	0
Denominator for diluted loss per share - adjusted weighted average shares and after assumed exercises (in shares)										91,500	91,000	87,100
Loss per share - Basic (in dollars per share)		$ 0.53	$ (0.89)	$ (0.05)	$ (0.22)	$ (2.41)	$ (0.65)	$ (0.33)	$ (0.42)	$ (0.63)	$ (3.81)	$ (2.91)
Loss per share - Diluted (in dollars per share)		$ 0.53	$ (0.89)	$ (0.05)	$ (0.22)	$ (2.41)	$ (0.65)	$ (0.33)	$ (0.42)	$ (0.63)	$ (3.81)	$ (2.91)
Conversion of convertible preferred stock to common stock, (in shares)	4,700
Series A Mandatory Convertible Preferred Stock
Effect of dilutive securities:
Conversion of convertible preferred stock to common stock, (in shares)												1,400
Antidilutive shares excluded from computation of diluted (loss) earnings per share (in shares)												3,367
Stock Options
Effect of dilutive securities:
Shares and awards excluded from computation of diluted (loss) earnings per share due to net loss incurred (in shares)										264	74	124
Antidilutive shares excluded from computation of diluted (loss) earnings per share (in shares)										3,017	4,507	4,664