Selected Quarterly Financial Data (unaudited) (Details) - USD ($) $ / shares in Units, $ 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
Quarterly Financial Data [Abstract]
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
Operating Profit	111.9	76.4	(1.0)	26.2	73.3	52.5	52.6	58.4	213.5		236.8		274.7
Amounts attributable to Brink’s:
Continuing operations	25.1	(23.8)	13.7	1.8	(3.8)	5.8	12.6	13.7	16.8		28.3		(33.3)
Discontinued operations	0.1	(0.1)	(0.8)	0.0	1.2	(0.4)	(0.1)	0.0	(0.8)		0.7		0.0
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)
Depreciation and amortization	54.6	55.1	52.1	45.0	45.5	42.9	48.7	47.9	206.8		185.0		162.3
Capital expenditures	$ 39.4	$ 25.2	$ 23.7	$ 30.2	$ 48.8	$ 42.9	$ 37.9	$ 35.2	$ 118.5		$ 164.8		$ 155.1
Basic
Continuing operations (in dollars per share)	$ 0.51	$ (0.47)	$ 0.27	$ 0.04	$ (0.08)	$ 0.11	$ 0.25	$ 0.27	$ 0.33	[1]	$ 0.56	[1]	$ (0.65)	[1]
Discontinued operations (in dollars per share)	0	0	(0.02)	0	0.02	(0.01)	0	0	(0.02)	[1]	0.01	[1]	0	[1]
Net income (loss) (in dollars per share)	0.51	(0.48)	0.25	0.03	(0.05)	0.11	0.25	0.27	0.32	[1]	0.58	[1]	(0.65)	[1]
Diluted
Continuing operations (in dollars per share)	0.50	(0.47)	0.27	0.03	(0.08)	0.11	0.25	0.27	0.33	[1]	0.55	[1]	(0.65)	[1]
Discontinued operations (in dollars per share)	0	0	(0.01)	0	0.02	(0.01)	0	0	(0.02)	[1]	0.01	[1]	0	[1]
Net income (loss) (in dollars per share)	$ 0.50	$ (0.48)	$ 0.25	$ 0.03	$ (0.05)	$ 0.10	$ 0.25	$ 0.27	$ 0.31	[1]	$ 0.57	[1]	$ (0.65)	[1]
Effect of Fourth Quarter Events [Line Items]
Derivative instrument losses				$ 7.7					$ (7.0)		$ 0.0		$ 0.0
Gain on sale of business									4.1		0.0		11.2
Gain (loss) on equity securities	$ 8.1		$ 5.8						10.6		(2.9)		3.2
Foreign currency transaction losses									(11.2)		(22.9)		(13.9)
Share-based expense for modification							$ 6.9		32.7		42.7		28.2
Gain on lease termination							5.2		0.0		5.2
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
Brazil social tax credit									0.4		0.3		0.6
Other Restructurings
Effect of Fourth Quarter Events [Line Items]
Restructuring costs											28.8
Operating Income (Loss) | Severance Costs | Other Restructurings
Effect of Fourth Quarter Events [Line Items]
Restructuring costs	16.9		$ 39.0						66.6
Brazil
Quarterly Financial Data [Abstract]
Revenues									315.0		440.4		405.4
Effect of Fourth Quarter Events [Line Items]
Revenues									315.0		440.4		405.4
Brazil social tax credit					8.2
ARGENTINA
Quarterly Financial Data [Abstract]
Revenues									171.2		214.4		247.2
Effect of Fourth Quarter Events [Line Items]
Revenues									171.2		214.4		247.2
Argentina, Pesos | ARGENTINA
Effect of Fourth Quarter Events [Line Items]
Foreign currency transaction losses		$ 10.4							10.4		4.7
French security services company
Effect of Fourth Quarter Events [Line Items]
Gain on sale of business	(0.2)			$ 4.7					4.5
Internal Loss AR Rebuild
Quarterly Financial Data [Abstract]
Revenues						4.0
Effect of Fourth Quarter Events [Line Items]
Revenues						4.0
Bank fees						0.3
Increase to bad debt expense					6.4	13.7			6.6
Immaterial error correction						$ 10.0
Pension plan
Effect of Fourth Quarter Events [Line Items]
Settlement charge									(2.4)		(21.4)		(1.7)
U.S. Plans
Effect of Fourth Quarter Events [Line Items]
Settlement charge									$ 0.0		$ (19.3)		$ 0.0
U.S. Plans | Pension plan
Effect of Fourth Quarter Events [Line Items]
Settlement charge	$ 19.3				$ 19.3

[1] Amounts may not add due to rounding.