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Note 5 - Retirement Plans (Details Textual)	6 Months Ended
	Jun. 30, 2022
Defined Benefit Plan, Expected Return on Plan Assets, Changes In Fair Value, Period (Year)	5 years

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