Shareholders' Equity | Company's Common Share Repurchase and Issuance Activity (Details) - $ / shares	3 Months Ended	6 Months Ended
	Jul. 31, 2017	Jul. 31, 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 July 31, 2017	21,100,662	21,100,662
Treasury Stock Held, Average Cost Per Share	$ 44.59	$ 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		132,919