Long-term Debt (New Long-term Debt Issuances) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Apr. 30, 2011
Long-term debt, Principal Amount	$ 5,000
1.625% Debt due April 15, 2014 [Member]
Long-term debt, Issue Date	April 18, 2011
Long-term debt, Maturity Date	Apr. 15, 2014
Long-term debt, Interest Rate	1.625%
Long-term debt, Principal Amount	1,000
2.800% Debt due April 15, 2016 [Member]
Long-term debt, Issue Date	April 18, 2011
Long-term debt, Maturity Date	Apr. 15, 2016
Long-term debt, Interest Rate	2.80%
Long-term debt, Principal Amount	1,000
4.250% Debt due April 15, 2021 [Member]
Long-term debt, Issue Date	April 18, 2011
Long-term debt, Maturity Date	Apr. 15, 2021
Long-term debt, Interest Rate	4.25%
Long-term debt, Principal Amount	1,000
5.625% Debt due April 15, 2041 [Member]
Long-term debt, Issue Date	April 18, 2011
Long-term debt, Maturity Date	Apr. 15, 2041
Long-term debt, Interest Rate	5.625%
Long-term debt, Principal Amount	$ 2,000