Acquisitions and Dispositions - Pro Forma (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Business Acquisition [Line Items]
Actual revenue results included in consolidation	$ 206.0	$ 123.5	$ 362.4	$ 128.9
Actual net income results included in consolidation	1.1	2.6	6.7	3.0
Revenues	1,048.8	826.0	2,026.5	1,698.8
Net income (loss) attributable to Brink’s	23.9	12.9	36.6	14.7
Pro forma revenue results	1,048.8	887.8	2,064.9	1,957.0
Pro forma net income results	23.9	10.0	39.8	14.2
Transaction costs	4.3	16.1	4.3	16.1
PAI
Business Acquisition [Line Items]
Actual revenue results included in consolidation	34.0		34.0
Actual net income results included in consolidation	2.5		2.5
Pro forma revenue results		20.9	31.4	44.2
Pro forma net income results		0.0	2.5	0.4
G4S
Business Acquisition [Line Items]
Actual revenue results included in consolidation	172.0	123.5	328.4	128.9
Actual net income results included in consolidation	$ (1.4)	2.6	4.2	3.0
Pro forma revenue results		40.9	7.0	214.0
Pro forma net income results		$ (2.9)	$ 0.7	$ (0.9)