Debt - Carrying Value of Borrowings (Details) - USD ($) $ in Millions	Jul. 31, 2020	Jan. 31, 2020
Debt Instrument [Line Items]
Total carrying value of debt	$ 2,676	$ 2,677
Less current portion of debt	(3)	(4)
Total noncurrent debt	$ 2,673	2,673
Senior Notes \| 2023 Senior Notes
Debt Instrument [Line Items]
Effective interest rate for the three months ended July 31, 2020	3.26%
Total carrying value of debt	$ 995	995
Senior Notes \| 2028 Senior Notes
Debt Instrument [Line Items]
Effective interest rate for the three months ended July 31, 2020	3.70%
Total carrying value of debt	$ 1,490	1,489
Secured Debt \| Loan assumed on 50 Fremont
Debt Instrument [Line Items]
Effective interest rate for the three months ended July 31, 2020	3.75%
Total carrying value of debt	$ 191	$ 193

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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