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.