Acquisitions and Dispositions - Pro Forma (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Business Acquisition [Line Items]
Actual revenue results included in consolidation	$ 156.4	$ 5.4
Actual net income results included in consolidation	5.6	0.4
Revenues	977.7	872.8
Net income (loss) attributable to Brink’s	12.7	1.8
Pro forma revenue results	984.7	1,045.9
Pro forma net income results	13.4	3.8
Transaction costs	2.4	5.5
G4S
Business Acquisition [Line Items]
Actual revenue results included in consolidation	156.4	5.4
Actual net income results included in consolidation	5.6	0.4
Pro forma revenue results	7.0	173.1
Pro forma net income results	$ 0.7	$ 2.0