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=84234895&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=82849420&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	9 Months Ended		12 Months Ended
	Oct. 31, 2017 JPY (¥)	Oct. 31, 2017 GBP (£)	Jan. 31, 2017 JPY (¥)	Jan. 31, 2017 GBP (£)	Oct. 31, 2017 USD ($)	Jan. 31, 2017 USD ($)
Derivative [Line Items]
Cash collateral held from counterparties					$ 251	$ 242
Threshold of derivative liability position requiring cash collateral					$ 150
Designated as hedging instrument \| Net investment hedging \| Japan
Derivative [Line Items]
Notional amount of nonderivative instruments \| ¥	¥ 180		¥ 10
Designated as hedging instrument \| Net investment hedging \| United Kingdom
Derivative [Line Items]
Notional amount of nonderivative instruments \| £		£ 2.1		£ 2.5