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Note 17 - Commitments and Contingencies (Details Textual) $ in Thousands	12 Months Ended
	Dec. 31, 2021 USD ($)
Sites Identified	376
Sites Subject of Actions Taken by US Government	28
Sites on Superfund National Priorities List	18
Personal Injury [Member]
Recorded Liability Related to Asserted Claims	94.00%
Recorded Liability Related to Unasserted Claims	6.00%
Personal Injury [Member] | Minimum [Member]
Loss Contingency, Estimate of Possible Loss	$ 325
Personal Injury [Member] | Maximum [Member]
Loss Contingency, Estimate of Possible Loss	$ 358

X

- Definition

Information on the percentage of recorded liability that relates to asserted claims.

+ References

No definition available.

+ Details

Name:	unp_RecordedLiabilityRelatedToAssertedClaims
Namespace Prefix:	unp_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Information on the percentage of recorded liability that relates to un-asserted claims.

+ References

No definition available.

+ Details

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Namespace Prefix:	unp_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Sites identified at which Railroad is or may be liable for remediation costs associated with alleged contamination or for violations of environmental requirements.

+ References

No definition available.

+ Details

Name:	unp_SitesIdentified
Namespace Prefix:	unp_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Sites on the Superfund National Priorities List.

+ References

No definition available.

+ Details

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Namespace Prefix:	unp_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Sites subject of actions taken by the U.S. government.

+ References

No definition available.

+ Details

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Namespace Prefix:	unp_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121557415&loc=d3e14435-108349

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 9
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121557415&loc=d3e14557-108349

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=124440162&loc=d3e12021-110248

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Balance Type:	debit
Period Type:	instant

X

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
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Balance Type:
Period Type:

X

- Details

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Namespace Prefix:
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