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v3.23.1

Note 4 - Retirement Plans (Details Textual) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2023 | Dec. 31, 2022
Defined Benefit Plan, Expected Return on Plan Assets, Changes In Fair Value, Period (Year) |  | 5 years
Payment for Pension Benefits | $ 0 |

X
- Definition The expected long-term rate of return on plan assets that is applied to a calculated value of plan assets that recognizes the changes in fair value over this period. + References No definition available. + Details
Name: | unp_DefinedBenefitPlanExpectedReturnOnPlanAssetsChangesInFairValuePeriod
Namespace Prefix: | unp_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of cash outflow for pension benefit. Includes, but is not limited to, employer contribution to fund plan asset and payment to retiree. Excludes other postretirement benefit. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 45 -Paragraph 25 -Subparagraph (g) -SubTopic 10 -Topic 230 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482740/230-10-45-25 + Details
Name: | us-gaap_PensionContributions
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration