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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226016-175313

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=d3e41678-113959

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-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

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	3 Months Ended		6 Months Ended
	Jan. 31, 2019 JPY (¥)	Jan. 31, 2019 GBP (£)	Jul. 31, 2019 JPY (¥)	Jul. 31, 2019 GBP (£)	Jul. 31, 2019 USD ($)	Jan. 31, 2019 USD ($)
Derivative [Line Items]
Cash collateral held from counterparties					$ 216	$ 220
Threshold of derivative liability position requiring cash collateral					$ 150
Designated as hedging instrument \| Net investment hedging [Member] \| Japan
Derivative [Line Items]
Notional amount of nonderivative instruments \| ¥	¥ 180		¥ 180
Designated as hedging instrument \| Net investment hedging [Member] \| United Kingdom
Derivative [Line Items]
Notional amount of nonderivative instruments \| £		£ 1.7		£ 1.7