Debt - Short-Term Debt (Details) (USD $) In Millions, unless otherwise specified	Jan. 31, 2015
U.S. revolving credit facility [Member]
Short-term Debt
Line of credit facility, amount outstanding	$ 0
U.S. revolving credit facility - 364-Day [Member]
Short-term Debt
Line of Credit Facility, Previous Borrowing Capacity	500
U.S. revolving credit facility - Five-Year [Member]
Short-term Debt
Line of Credit Facility, Previous Borrowing Capacity	1,500
Line of credit facility, current borrowing capacity	$ 1,250
Debt instrument, basis spread on federal funds rate (as a percent)	0.50%
Debt instrument, basis spread on LIBOR (as a percent)	1.00%
Debt instrument, lower range on ABR (as a percent)	0.00%
Debt instrument, higher range on ABR (as a percent)	0.925%
LIBOR margin, low end of the range (as a percent)	1.00%
LIBOR margin, high end of the range (as a percent)	1.925%
Debt instrument, lower range on facility fee (as a percent)	0.125%
Debt instrument, higher range on facility fee (as a percent)	0.325%