Shareholders' equity - Dividends (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	May 02, 2020	May 04, 2019
Dividends Payable [Line Items]
Dividends declared per common share (usd per share)	$ 0.00	$ 0.37
Dividends, common stock	$ 0.0	$ 19.3
Dividends declared per preferred share (usd per share)	$ 12.50	$ 12.50
Dividends, preferred stock, paid-in-kind	$ 7.8
Dividends, preferred stock		$ 7.8
Common Stock | Accrued expenses and other current liabilities
Dividends Payable [Line Items]
Dividends payable		19.3
Series A Redeemable Convertible Preferred Stock | Accrued expenses and other current liabilities
Dividends Payable [Line Items]
Dividends payable	$ 7.8	$ 7.8