FINANCIAL SERVICES - Credit Quality Indicators (Details) - USD ($) $ in Millions	Jul. 31, 2020	Jan. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Customer receivables, gross	$ 10,033
Fixed-term | Fixed-term — Consumer and Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2021	3,200
2020	3,698
2019	1,788
2018	482
2017	83
Years Prior	4
Customer receivables, gross		$ 8,486
Revolving
Financing Receivable, Credit Quality Indicator [Line Items]
Customer receivables, gross		9,310
Revolving | Revolving — DPA
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, revolving	598
Customer receivables, gross		621
Revolving | Revolving — DBC
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, revolving	180
Customer receivables, gross		203
Higher
Financing Receivable, Credit Quality Indicator [Line Items]
Customer receivables, gross	5,792
Higher | Fixed-term | Fixed-term — Consumer and Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2021	2,019
2020	2,265
2019	992
2018	273
2017	43
Years Prior	1
Customer receivables, gross		5,042
Higher | Revolving
Financing Receivable, Credit Quality Indicator [Line Items]
Customer receivables, gross		5,234
Higher | Revolving | Revolving — DPA
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, revolving	148
Customer receivables, gross		137
Higher | Revolving | Revolving — DBC
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, revolving	51
Customer receivables, gross		55
Mid
Financing Receivable, Credit Quality Indicator [Line Items]
Customer receivables, gross	2,250
Mid | Fixed-term | Fixed-term — Consumer and Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2021	633
2020	824
2019	417
2018	127
2017	20
Years Prior	1
Customer receivables, gross		2,036
Mid | Revolving
Financing Receivable, Credit Quality Indicator [Line Items]
Customer receivables, gross		2,274
Mid | Revolving | Revolving — DPA
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, revolving	176
Customer receivables, gross		175
Mid | Revolving | Revolving — DBC
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, revolving	52
Customer receivables, gross		63
Lower
Financing Receivable, Credit Quality Indicator [Line Items]
Customer receivables, gross	1,991
Lower | Fixed-term | Fixed-term — Consumer and Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2021	548
2020	609
2019	379
2018	82
2017	20
Years Prior	2
Customer receivables, gross		1,408
Lower | Revolving
Financing Receivable, Credit Quality Indicator [Line Items]
Customer receivables, gross		1,802
Lower | Revolving | Revolving — DPA
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, revolving	274
Customer receivables, gross		309
Lower | Revolving | Revolving — DBC
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, revolving	$ 77
Customer receivables, gross		$ 85