Shareholders' Equity | Company's Common Share Repurchase and Issuance Activity (Details) - $ / shares	3 Months Ended
	Apr. 30, 2017	Jan. 31, 2017
Increase (Decrease) in Treasury Stock
Treasury stock balance at January 31, 2017	24,018,983
Treasury Stock, Shares, Acquired	0
Treasury stock balance at April 30, 2017	21,117,840
Treasury Stock Held, Average Cost Per Share	$ 44.59	$ 44.59
TS
Increase (Decrease) in Treasury Stock
Shares of treasury stock reissued	2,785,402
Equity Incentive Plans
Increase (Decrease) in Treasury Stock
Shares of treasury stock reissued	115,741