Employee Stock and Savings Plans and Stockholders Equity Weighting of elements included in volatility assumption (Details)	12 Months Ended
	Jan. 31, 2013
Common Stock
Weighting of elements used in determining volatility assumption	20.00%
Exchange Traded Options
Weighting of elements used in determining volatility assumption	15.00%
Common Stock
Weighting of elements used in determining volatility assumption	35.00%
Exchange Traded Options
Weighting of elements used in determining volatility assumption	30.00%