Derivative Financial Instruments (Narrative) (Details)	3 Months Ended			3 Months Ended						3 Months Ended
	Apr. 30, 2013 USD ($)	Jan. 31, 2013 USD ($)	Jan. 31, 2013 GBP (£)	Apr. 30, 2013 Cash Flow Hedging [Member] USD ($)	Apr. 30, 2013 Fair Value Hedging [Member]	Apr. 30, 2013 Net Investment Hedging [Member]	Apr. 30, 2013 Net Investment Hedging [Member] United Kingdom and Japan [Member]	Apr. 30, 2013 Net Investment Hedging [Member] United Kingdom [Member] GBP (£)	Apr. 30, 2013 Net Investment Hedging [Member] JAPAN JPY (¥)	Apr. 30, 2013 Cash Flow Hedging [Member]	Apr. 30, 2013 Cash Flow Hedging [Member] Interest Rate Swap [Member]	Apr. 30, 2013 Cash Flow Hedging [Member] Cross Currency Interest Rate Contract [Member]	Apr. 30, 2013 Netting and Collateral [Member] USD ($)	Jan. 31, 2013 Netting and Collateral [Member] USD ($)
Derivative [Line Items]
Derivative, Collateral, Obligation to Return Cash													$ 399,000,000	$ 413,000,000
Threshold of derivative liability position requiring cash collateral	150,000,000
Investment maturity date range start					May 30, 2013	Oct. 30, 2023	Aug. 31, 2013				Aug. 30, 2013	Sep. 30, 2029
Investment maturity date range end					May 31, 2014	Feb. 28, 2030	Jan. 31, 2039				Jul. 30, 2015	Mar. 30, 2034
Debt designated as United Kingdom net investment hedge			2,500,000,000					2,500,000,000
Debt designated as Japanese net investment hedge		275,000,000,000							275,000,000,000
Forward Starting Interest Rate Swap Number of Years Hedging Minimum	10
Forward Starting Interest Rate Swap Number of Years Hedging Maximum	30
Forward Starting Interest Rate Swap Termination Date										Oct. 31, 2014
Notional Amount				2,500,000,000
Cash payment for terminated derivatives				74,000,000
Deferred (Gain) Loss on Discontinuation of Cash Flow Hedge				$ 74,000,000