Derivative Financial Instruments (Narrative) (Details) $ in Millions, ¥ in Billions, £ in Billions	3 Months Ended
	Apr. 30, 2016 JPY (¥)	Apr. 30, 2016 GBP (£)	Apr. 30, 2016 USD ($)	Jan. 31, 2016 USD ($)
Derivative [Line Items]
Cash collateral held from counterparties | $			$ 349	$ 345
Threshold of derivative liability position requiring cash collateral | $			$ 150
Net investment hedging | Japan
Derivative [Line Items]
Notional amount of nonderivative instruments | ¥	¥ 10
Net investment hedging | United Kingdom
Derivative [Line Items]
Notional amount of nonderivative instruments | £		£ 2.5
Designated as hedging instrument | Net investment hedging | Japan
Derivative [Line Items]
Notional amount of nonderivative instruments | ¥	¥ 10
Designated as hedging instrument | Net investment hedging | United Kingdom
Derivative [Line Items]
Notional amount of nonderivative instruments | £		£ 2.5