Basis of presentation (Details) $ in Millions		3 Months Ended			6 Months Ended	9 Months Ended
		Sep. 30, 2018 USD ($) $ / $	Jun. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Sep. 30, 2018 USD ($) segment $ / $	Sep. 30, 2017 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) $ / $	Dec. 31, 2016 $ / $
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of operating segments | segment						3
Loss on deconsolidation of Venezuela operations		$ 0.0		$ 0.0		$ (126.7)	$ 0.0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Deconsolidation, pretax		(14.3)		$ (13.6)		(159.2)	(39.6)
Net monetary liabilities		2,940.5				2,940.5			$ 2,721.4
Cash and cash equivalents		314.2				314.2			614.3
Accumulated other comprehensive losses related to Venezuela		918.0				918.0			926.6
Net monetary assets		1,174.2				1,174.2			1,488.2
Goodwill		$ 651.9				651.9			453.7
Cumulative effect of change in accounting principle	[1]							$ 2.2
Net Cash Provided by Operating Activities						148.6	137.0
Net Cash Provided by Financing Activities						184.3	225.1
Effect of exchange rate changes on cash						$ (29.6)	$ 2.8
Venezuelan bolívar fuerte | Venezuela
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loss on deconsolidation of Venezuela operations			$ 127.0
Derecognition of the carrying amounts of assets included in the deconsolidation charge			32.0
Derecognition of the carrying amounts of liabilities included in the deconsolidation charge			$ 11.0
Rate decrease percent			97.00%	80.00%	97.00%		80.00%
Net remeasurement loss					$ 2.2		$ (9.1)
Income (loss) attributable to noncontrolling interest					$ 2.0		1.0
Net monetary liabilities									2.3
Cash and cash equivalents									3.4
Accumulated other comprehensive losses related to Venezuela									$ 114.9
Argentine pesos | Argentina
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Rate decrease percent		55.00%				55.00%			15.00%
Net remeasurement loss		$ (8.1)
Nonmonetary assets		147.6				$ 147.6
Cash and cash equivalents		$ 11.1				$ 11.1
Percent of Consolidated Revenue						8.00%
Official exchange rate | $ / $		41.3				41.3			18.6	15.9
Net monetary assets		$ 19.3				$ 19.3
Goodwill		98.7				98.7
Equity Securities		0.0				0.0
Venezuela Investment | Venezuelan bolívar fuerte | Venezuela
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Investment in Venezuela operations									$ 23.1
Net payables to other Brink's affiliates									2.7
Nonmonetary assets									23.0
Foreign currency translation adjustments
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Deconsolidation, pretax		$ 0.0		$ 0.0		$ (107.2)	0.0
Foreign currency translation adjustments | Venezuelan bolívar fuerte | Venezuela
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Deconsolidation, pretax			$ 106.0
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of change in accounting principle	[1]							$ 3.3
Accounting Standards Update 2014-09 | Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of change in accounting principle									1.5
Accounting Standards Update 2016-01 | Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of change in accounting principle									1.1
Accounting Standards Update 2016-16 | Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of change in accounting principle									$ 0.7
Accounting Standards Update 2016-18
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net Cash Provided by Operating Activities							20.8
Net Cash Provided by Financing Activities							0.3
Effect of exchange rate changes on cash							$ 9.7

[1] Effective January 1, 2018, we adopted the provisions of ASU 2014-09, Revenue From Contracts with Customers, ASU 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities, and ASU 2016-16, Intra-Entity Transfers of Assets Other Than Inventory. We recognized a cumulative effect adjustment to January 1, 2018 retained earnings as a result of adopting each of these standards. See Note 1 for further details of the impact of each standard.