Stock-based Compensation Expense Summary of ESPP Activity (Details) - Employee Stock - Employee Qualified Stock Purchase Plan 1998 ESP Plan - $ / shares shares in Millions	3 Months Ended		9 Months Ended
	Oct. 31, 2017	Oct. 31, 2016	Oct. 31, 2017	Oct. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issued shares	0.9	1.1	2.0	2.3
Average price of issued shares (in dollars per share)	$ 39.92	$ 37.36	$ 39.03	$ 36.99
Weighed average grant date fair value of awards granted under the ESPP (in dollars per share)	$ 33.04	$ 20.75	$ 32.41	$ 19.20