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Subsequent Event (Details) - $ / shares
12 Months Ended
Feb. 18, 2016
Jan. 31, 2016
Jan. 31, 2015
Jan. 31, 2014
Subsequent Event [Line Items]        
Dividends declared per common share   $ 1.96 $ 1.92 $ 1.88
Subsequent event        
Subsequent Event [Line Items]        
Dividends declared per common share $ 2.00      
Common stock, quarterly dividends, per share, declared $ 0.50