Debt (Equipment Encumbrances) (Narrative) (Details) - USD ($) $ in Billions	Dec. 31, 2019	Dec. 31, 2018
Debt [Abstract]
Carrying value of equipment serving as collateral for finance leases and other types of equipment obligations	$ 1.6	$ 1.8

Carrying value of equipment serving as collateral for finance leases and other types of equipment obligations.

No definition available.

Name:	unp_CarryingValueOfEquipmentServingAsCollateralForFinanceLeasesAndOtherTypesOfEquipmentObligations
Namespace Prefix:	unp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant