Name:	unp_AllowableDebtPerDebtToNetWorthCoverageRatioAsDefinedFacility
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Data Type:	xbrli:monetaryItemType
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Period Type:	instant

Amount of debt issuance authorized by Board of Directors.

No definition available.

Name:	unp_BoardOfDirectorsAuthorizedDebtIssuance
Namespace Prefix:	unp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of debt issuance remaining under current authority by Board of Directors.

No definition available.

Name:	unp_BoardOfDirectorsRemainingDebtIssuance
Namespace Prefix:	unp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Maximum duration of commercial paper maturities, in 'PnYnMnDTnHnMnS' format, for example, P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

No definition available.

Name:	unp_CommercialPaperMaturityDurationMaximum
Namespace Prefix:	unp_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Minimum duration of commercial paper maturities, in 'PnYnMnDTnHnMnS' format, for example, P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

No definition available.

Name:	unp_CommercialPaperMaturityDurationMinimum
Namespace Prefix:	unp_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Cross-default provision, as defined by facility.

No definition available.

Name:	unp_CrossDefaultProvisionAsDefinedByFacility
Namespace Prefix:	unp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Outstanding debt as defined by the credit facility.

No definition available.

Name:	unp_OutstandingDebtAsDefinedByFacility
Namespace Prefix:	unp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Carrying value as of the balance sheet date of short-term borrowings using unsecured obligations issued by banks, corporations and other borrowers to investors. The maturities of these money market securities generally do not exceed 270 days.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
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Name:	us-gaap_CommercialPaper
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Data Type:	xbrli:monetaryItemType
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Period Type:	instant

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.

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-Topic 470
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
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Name:	us-gaap_LineOfCredit
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Period Type:	instant

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
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-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
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-Subparagraph (a)
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Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(f))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480678/235-10-S99-1

Name:	us-gaap_LineOfCreditFacilityLineItems
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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
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-Topic 210
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-Name Accounting Standards Codification
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-Subparagraph (SX 210.5-02(22)(b))
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-Subparagraph (SX 210.5-02(19)(b))
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Name:	us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
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Data Type:	xbrli:monetaryItemType
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Period Type:	instant

The cash inflow from borrowing by issuing commercial paper.

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-Topic 230
-SubTopic 10
-Section 45
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Name:	us-gaap_ProceedsFromIssuanceOfCommercialPaper
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

The cash outflow due to repaying amounts borrowed by issuing commercial paper.

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