Debt (Narrative) (Details) (USD $) In Billions, unless otherwise specified	6 Months Ended
	Jul. 31, 2011
Aggregate net proceeds from note issuances	$ 4.9
Date of first repayment of long-term debt	October 15, 2011
Repayment of debt, percentage of principal amount under normal conditions	100.00%
364 Days Facility [Member] | Revolving Credit Facility [Member]
Maximum borrowing capacity of credit facility	10.00
364 Days Facility [Member] | Revolving Credit Facility [Member] | As Previously Reported [Member]
Maximum borrowing capacity of credit facility	9.00
5-Year Facility [Member] | Revolving Credit Facility [Member]
Maximum borrowing capacity of credit facility	6.30
5-Year Facility [Member] | Revolving Credit Facility [Member] | As Previously Reported [Member]
Maximum borrowing capacity of credit facility	4.30
Letter Of Credit [Member] | As Previously Reported [Member]
Maximum borrowing capacity of credit facility	$ 2.20