Basis of Presentation Reclassification (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jul. 31, 2016	Apr. 30, 2016	Jul. 31, 2015	Jul. 31, 2016	Jul. 31, 2015
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Provision for income taxes	$ 25.2	$ (14.4)	$ 269.5	$ 39.6	$ 272.2
Operating expenses	$ 528.5		512.2	$ 1,097.7	1,045.4
Employee Benefits and Estimated Personal Property Liabilities
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Operating expenses					5.7
Restatement Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Provision for income taxes			$ 33.1		$ 33.1