Amount of obligation to return cash collateral under master netting arrangements that have not been offset against derivative assets.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=d3e41678-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (d)(2)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=51825145&loc=SL20226016-175313

Name:	us-gaap_DerivativeCollateralObligationToReturnCash
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Derivative Financial Instruments (Narrative) (Details) $ in Millions, ¥ in Billions, £ in Billions	12 Months Ended
	Jan. 31, 2017 JPY (¥)	Jan. 31, 2017 GBP (£)	Jan. 31, 2016 JPY (¥)	Jan. 31, 2016 GBP (£)	Jan. 31, 2017 USD ($)	Jan. 31, 2016 USD ($)
Derivative [Line Items]
Cash collateral held from counterparties					$ 242	$ 345
Threshold of derivative liability position requiring cash collateral					$ 150
Designated as hedging instrument \| Net investment hedging \| United Kingdom
Derivative [Line Items]
Notional amount of nonderivative instruments \| £		£ 2.5		£ 2.5
Designated as hedging instrument \| Net investment hedging \| Japan
Derivative [Line Items]
Notional amount of nonderivative instruments \| ¥	¥ 10.0		¥ 10.0