Summary of Significant Accounting Policies (Narrative) (Details) $ in Millions	12 Months Ended
	Jan. 31, 2021 USD ($) segment	Jan. 31, 2020 USD ($)	Jan. 31, 2019 USD ($)
Accounting Policies [Line Items]
Number of reportable segments | segment	3
Cash and cash equivalents	$ 17,741	$ 9,465
Percentage of cash and cash equivalents	40.00%	80.00%
Receivables from transactions with customers, net	$ 2,700	$ 2,900
Liabilities for sale	12,734	0
Depreciation and amortization	11,152	10,987	$ 10,678
Indefinite-lived intangible assets (excluding goodwill)	$ 4,900	5,200
Impairment of intangible assets (excluding goodwill)		700
Global intangible low-taxed income, 2018 through 2025	10.50%
Global intangible low-taxed income, 2025 thereafter	13.125%
Membership fee revenue	$ 3,918	4,038	4,076
Advertising expense	3,200	3,700	3,500
Membership Fees [Member]
Accounting Policies [Line Items]
Membership fee revenue	1,700	1,500	$ 1,400
Amounts Due from Banks [Member]
Accounting Policies [Line Items]
Cash and cash equivalents	4,100	1,700
Nonrepatriable Cash and Cash Equivalents [Member]
Accounting Policies [Line Items]
Cash and cash equivalents	2,800	2,300
Prepaid Expenses and Other [Member]
Accounting Policies [Line Items]
Discontinued operation, current assets	19,200
Accrued Liabilities [Member]
Accounting Policies [Line Items]
Liabilities for sale	12,700
Long-term Debt [Member] | Net Investment Hedging [Member]
Accounting Policies [Line Items]
Nonderivative hedging instruments	3,300	$ 3,900
Flipkart [Member] | Nonrepatriable Cash and Cash Equivalents - Flipkart [Member]
Accounting Policies [Line Items]
Cash and cash equivalents	$ 1,000