Document and Entity Information - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2019	Jan. 31, 2020	Jun. 28, 2019
Document and Entity Information [Abstract]
Document type	10-K
Document Annual Report	true
Document period end date	Dec. 31, 2019
Document Transition Report	false
Amendment flag	false
Entity registrant name	UNION PACIFIC CORPORATION
Entity central index key	0000100885
Entity current reporting status	Yes
Entity voluntary filers	No
Entity Interactive Data Current	Yes
Current fiscal year end date	--12-31
Entity filer category	Large Accelerated Filer
Entity well known seasoned issuer	Yes
Entity public float			$ 119.0
Document fiscal year focus	2019
Document fiscal period focus	FY
Title of 12(b) Security	Common Stock (Par Value $2.50 per share)
Trading Symbol	UNP
Security Exchange Name	NYSE
Entity common stock shares outstanding		690,261,490
Entity Shell Company	false
Entity Emerging Growth Company	false
Entity Small Business	false
Entity File Number	1-6075
Entity Incorporation, State or Country Code	UT
Entity Tax Identification Number	13-2626465
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