Income Taxes - Reconciliation of Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2017
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits at beginning of year	$ 10.1	$ 7.2	$ 14.0
Gross increases – tax positions in prior period	8.0	3.2	0.9
Gross decreases – tax positions in prior period	0.0	(0.9)	(5.0)
Gross increases – tax positions in current period	1.3	0.6	0.3
Settlements	0.0	0.0	(3.0)
Lapse of statute of limitations	(2.1)	0.0	0.0
Unrecognized tax benefits at end of year	$ 17.3	$ 10.1	$ 7.2