Shareholders' Equity Company's Common Share Repurchase and Issuance Activity (Details) - $ / shares	3 Months Ended
	Apr. 30, 2016	Jan. 31, 2016
Increase (Decrease) in Treasury Stock [Roll Forward]
Treasury stock balance at January 31, 2016	24,163,402
Treasury Stock, Shares, Acquired	0
Stock Issued During Period, Shares, Treasury Stock Reissued	(114,446)
Treasury stock balance at April 30, 2016	24,048,956
Treasury Stock Held, Average Cost Per Share	$ 44.59	$ 44.59