Derivative Financial Instruments (Narrative) (Details)				6 Months Ended
	Jul. 31, 2011 USD ($)	Jul. 31, 2011 JPY (¥)	Jan. 31, 2011 JPY (¥)	Jul. 31, 2011 Non-U.S. Denominated Debt [Member] Net Investment Instruments [Member]	Jul. 31, 2011 Non-U.S. Denominated Debt [Member] Cash Flow Instruments [Member]	Jul. 31, 2011 Fair Value Instruments [Member]	Jul. 31, 2011 Net Investment Instruments [Member]	Jul. 31, 2011 Cash Flow Instruments [Member]	Jul. 31, 2011 GBP [Member] GBP (£)	Jan. 31, 2011 GBP [Member] GBP (£)
Cash collateral held from counterparties	$ 492,000,000
Threshold of derivative liability position requiring cash collateral	150,000,000
Debt designated as United Kingdom net investment hedge									3,000,000,000	3,000,000,000
Debt designated as Japanese net investment hedge		¥ 300,000,000,000	¥ 300,000,000,000
Instrument maturity date range start				August 2011	September 2029	April 2012	October 2023	August 2013
Instrument maturity date range end				January 2039	March 2034	May 2014	February 2030	July 2015