Income Taxes - Tax Cuts and Jobs Act of 2017 (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2017
Income Tax Disclosure [Abstract]
Tax cuts and jobs act of 2017, estimated net tax expense	$ 146.2
Tax cuts and jobs act of 2017, incomplete accounting, change in tax rate, provisional income tax expense (benefit)	94.8
Tax cuts and jobs act of 2017 transition tax	56.0
Tax cuts and jobs act of 2017 statutory rate change	$ 4.6
Statutory Federal income tax rate		21.00%	33.80%	35.00%
Tax cuts and jobs act of 2017, measurement period adjustment, change in tax rate, income tax expense (benefit)		$ (12.6)
Tax cuts and jobs act of 2017, measurement period adjustment, income tax expense (benefit)		(3.3)
Undistributed foreign earnings		$ 900.0