Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2021	Jul. 16, 2021
Cover [Abstract]
Document type	10-Q
Document period end date	Jun. 30, 2021
Amendment flag	false
Entity registrant name	UNION PACIFIC CORPORATION
Entity central index key	0000100885
Entity current reporting status	Yes
Current fiscal year end date	--12-31
Entity filer category	Large Accelerated Filer
Document fiscal year focus	2021
Document fiscal period focus	Q2
Trading Symbol	UNP
Entity common stock shares outstanding		652,122,933
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Address, Address Line One	1400 Douglas Street
Entity Address, City or Town	Omaha
Entity Address, Postal Zip Code	68179
Entity Address, State or Province	NE
City Area Code	402
Local Phone Number	544-5000
Entity File Number	1-6075
Entity Tax Identification Number	13-2626465
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Stock (Par Value $2.50 per share)
Entity Incorporation, State or Country Code	UT
Security Exchange Name	NYSE
Document Quarterly Report	true
Document Transition Report	false