Derivative Financial Instruments (Narrative) (Details) - Derivative Contract Type [Domain] $ in Millions, ¥ in Billions, £ in Billions	6 Months Ended		12 Months Ended
	Jul. 31, 2015 JPY (¥)	Jul. 31, 2015 GBP (£)	Jan. 31, 2015 JPY (¥)	Jan. 31, 2015 GBP (£)	Jul. 31, 2015 USD ($)	Jan. 31, 2015 USD ($)
Derivative [Line Items]
Derivative, Collateral, Obligation to Return Cash					$ 330	$ 323
Threshold of derivative liability position requiring cash collateral					$ 150
Net Investment Hedging [Member] | United Kingdom [Member]
Derivative [Line Items]
Notional amount of nonderivative instruments | £				£ 2.5
Designated as Hedging Instrument [Member] | Net Investment Hedging [Member] | United Kingdom [Member]
Derivative [Line Items]
Notional amount of nonderivative instruments | £		£ 2.5
Designated as Hedging Instrument [Member] | Net Investment Hedging [Member] | JAPAN
Derivative [Line Items]
Notional amount of nonderivative instruments | ¥	¥ 10		¥ 100