Income taxes (Tables)

9 Months Ended

Sep. 30, 2018

Income Tax Disclosure [Abstract]

Schedule of Components of Income Tax Expense (Benefit)

	Three Months Ended September 30,					Nine Months Ended September 30,
	2018			2017		2018			2017
Continuing operations
Provision for income taxes (in millions)	$	23.0		16.4		$	53.0		48.1
Effective tax rate	54.9		%	43.7	%	(514.6		%)	39.0	%