| Document and Entity Information Document | Dec. 06, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Jul. 30, 2024 |
| Entity Registrant Name | Knight-Swift Transportation Holdings Inc. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-35007 |
| Entity Tax Identification Number | 20-5589597 |
| Entity Address, Address Line One | 2002 West Wahalla Lane |
| Entity Address, City or Town | Phoenix |
| Entity Address, State or Province | AZ |
| Entity Address, Postal Zip Code | 85027 |
| City Area Code | 602 |
| Local Phone Number | 269-2000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock $0.01 Par Value |
| Trading Symbol | KNX |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0001492691 |
| Amendment Flag | false |
