Income taxes (Tables)

6 Months Ended

Jun. 30, 2017

Income Tax Disclosure [Abstract]

Schedule of Components of Income Tax Expense (Benefit)

	Three Months Ended June 30,					Six Months Ended June 30,
	2017			2016		2017			2016
Continuing operations
Provision for income taxes (in millions)	$	17.3		14.5		$	31.7		23.9
Effective tax rate	56.0		%	81.0	%	36.9		%	89.2	%