Income taxes (Tables)
 9 Months Ended
Sep. 30, 2016
Income Tax Disclosure [Abstract]  
Schedule of Components of Income Tax Expense (Benefit)

Three Months Ended September 30,
 
Nine Months Ended September 30,
 
2016
 
2015
 
2016
 
2015
Continuing operations
 
 
 
 
 
 
 
Provision for income taxes (in millions)
$
19.5

 
14.1

 
$
43.4

 
37.2

Effective tax rate
43.0
%
 
65.9
%
 
60.1
%
 
341.3
%