| ASSETS HELD FOR SALE - Additional Information (Details) - UPS Freight Business - Held-for-sale - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended | |
|---|---|---|---|
| Mar. 31, 2021 | Dec. 31, 2020 | Jan. 24, 2021 | |
| Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] | |||
| Divestiture consideration | $ 800 | ||
| Impairment charges | $ 686 | ||
| Impairment charges, net of tax | 629 | ||
| Goodwill impairment charge | 494 | ||
| Increase in valuation allowance | $ 66 | $ 192 | |
| Increase in valuation allowance, after tax | $ 50 | 
| X | ||||||||||
| 
- Definition Asset Impairment Charges Net Of Tax No definition available. 
 | 
| X | ||||||||||
| 
- Definition Disposal Group, Not Discontinued Operation, Loss (Gain) On Write-Down Net Of Tax No definition available. 
 | 
| X | ||||||||||
| 
- Definition Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
 | 
| X | ||||||||||
| 
- Definition Amount of consideration received or receivable for the disposal of assets and liabilities, including discontinued operation. No definition available. 
 | 
| X | ||||||||||
| 
- Definition Amount, before tax, of (gain) loss recognized for the (reversal of write-down) write-down to fair value, less cost to sell, of a disposal group. Excludes discontinued operations. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
 | 
| X | ||||||||||
| 
- Definition Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
 | 
| X | ||||||||||
| 
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available. 
 | 
| X | ||||||||||
| 
- Details 
 | 
| X | ||||||||||
| 
- Details 
 |