Acquisitions and Dispositions Acquisitions and Dispositions - Pro Forma (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	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
Business Acquisition [Line Items]
Actual revenue results included in consolidation									$ 442.7	$ 82.1
Actual net income results included in consolidation									10.5	4.8
Revenues	$ 1,021.6	$ 970.5	$ 826.0	$ 872.8	$ 935.8	$ 928.4	$ 914.0	$ 905.0	3,690.9	3,683.2	$ 3,488.9
Reported net income (loss) attributable to Brink's	25.2	$ (23.9)	$ 12.9	$ 1.8	(2.6)	$ 5.4	$ 12.5	$ 13.7	16.0	29.0	(33.3)
Pro forma revenue results									3,882.9	4,450.6
Pro forma net income results									11.8	41.3
Transaction Costs	$ 19.3				$ 7.9				19.3	7.9	$ 6.7
G4S
Business Acquisition [Line Items]
Actual revenue results included in consolidation									442.7
Actual net income results included in consolidation									10.5
Pro forma revenue results									192.0	740.0
Pro forma net income results									$ (4.2)	10.7
Rodoban
Business Acquisition [Line Items]
Actual revenue results included in consolidation										66.0
Actual net income results included in consolidation										4.6
Pro forma revenue results										0.6
Pro forma net income results										0.0
Other Acquisitions
Business Acquisition [Line Items]
Actual revenue results included in consolidation										16.1
Actual net income results included in consolidation										0.2
Pro forma revenue results										26.8
Pro forma net income results										$ 1.6