Derivative instruments and hedging activities - Narrative (Details) $ in Millions		3 Months Ended
		Oct. 28, 2017 USD ($) interest_rate_caps open_foreign_currency_contracts	Jan. 28, 2017 USD ($) interest_rate_caps	Oct. 29, 2016 USD ($) interest_rate_caps
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount	[1]	$ 592	$ 789	$ 244
Other assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount		$ 507	560	50
Intercompany Loan [Member]
Derivatives, Fair Value [Line Items]
Number of Open Foreign Currency Forward Contracts | open_foreign_currency_contracts		0
Intercompany Loan [Member] | Not Designated as Hedging Instrument [Member] | Other Income [Member]
Derivatives, Fair Value [Line Items]
Gain (Loss) on Foreign Currency Derivative Instruments Not Designated as Hedging Instruments		$ 0
Foreign Exchange Contract [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative liabilities related to agreements that contain credit-risk related contingent features		$ 1	$ 1	$ 3
Cash Flow Hedging [Member] | Interest Rate Cap [Member]
Derivatives, Fair Value [Line Items]
Number of Interest Rate Derivatives Held | interest_rate_caps		1	2	1
Cash Flow Hedging [Member] | Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member] | Other assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount		$ 507	$ 0	$ 0

[1] Refer to Note 5 entitled “Fair value measurements” for the classification of our derivative instruments within the fair value hierarchy.