| Document and Entity Information | Mar. 09, 2021 |
| Cover [Abstract] | |
| Document type | 8-K |
| Document period end date | Mar. 9, 2021 |
| Amendment flag | false |
| Entity registrant name | UNION PACIFIC CORPORATION |
| Entity central index key | 0000100885 |
| Trading Symbol | UNP |
| Entity Emerging Growth 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 |
| Title of 12(b) Security | Common Stock (Par Value $2.50 per share) |
| Entity Incorporation, State or Country Code | UT |
| Security Exchange Name | NYSE |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
