Note 4 - Stock-based Compensation (Details Textual) shares in Thousands, $ in Millions	3 Months Ended
Mar. 31, 2024 USD ($) shares
Share-Based Payment Arrangement, Option [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Expiration Period (Year)	10 years
Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Period (Year)	3 years
Share-based Compensation Arrangement by Share-based Payment Award, Conditions (in shares) \| shares	0
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount	$ 30
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)	1 year 7 months 6 days
Retention Awards [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Period (Year)	4 years
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount	$ 118
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)	1 year 9 months 18 days
Performance Retention Awards [Member]
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount	$ 28
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)	2 years
Share-Based Compensation Arrangement by Share-Based Payment Award, Award Requisite Service Period (Month)	37 months
Share-based Compensation Arrangement by Share-based Payment Award, Performance Period (Year)	3 years

Represents the number of awards subject to performance or market-based vesting conditions.

No definition available.

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Namespace Prefix:	unp_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the performance period of share-based payment awards.

+ References

No definition available.

+ Details

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

- Definition

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

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Balance Type:	na
Period Type:	duration

- Details

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

- Details

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- Details

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