Debt (Narrative) (Details) (USD $) In Billions, unless otherwise specified	9 Months Ended
	Oct. 31, 2011
Debt Instrument [Line Items]
Aggregate net proceeds from note issuances	$ 4.9
Date of first repayment of long-term debt	2011-10-15
Repayment of debt, percentage of principal amount under normal conditions	100.00%
Letter Of Credit [Member] | As Previously Reported [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity of credit facility	2.2
364 Days Facility [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity of credit facility	10.0
364 Days Facility [Member] | Revolving Credit Facility [Member] | As Previously Reported [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity of credit facility	9.0
5-Year Facility [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity of credit facility	6.3
5-Year Facility [Member] | Revolving Credit Facility [Member] | As Previously Reported [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity of credit facility	$ 4.3