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Namespace Prefix:	unp_
Data Type:	xbrli:monetaryItemType
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Period Type:	duration

Amount of loss contingency liability.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 450
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483076/450-20-50-1

Reference 2: http://www.xbrl.org/2003/role/recommendedDisclosureRef
-Topic 450
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 10
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483076/450-20-50-10

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Period Type:	instant

Amount of loss contingency liability expected to be resolved within one year or the normal operating cycle, if longer.

Name:	us-gaap_LossContingencyAccrualCarryingValueCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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Amount of cash outflow reducing loss contingency liability.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 450
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483076/450-20-50-1

Name:	us-gaap_LossContingencyAccrualPayments
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Amount charged against operating income increasing loss contingency liability, after adjustments to reduce previously estimated charges.

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Data Type:	xbrli:monetaryItemType
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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

No definition available.