| Document and Entity Information Document - USD ($) | 12 Months Ended | ||
| Dec. 31, 2024 | Feb. 28, 2025 | Jun. 30, 2024 | |
| Cover [Abstract] | |||
| Document type | 10-K/A | ||
| Document annual report | true | ||
| Document period end date | Dec. 31, 2024 | ||
| Document transition report | false | ||
| Entity file number | 001-33378 | ||
| Entity registrant name | DISCOVER FINANCIAL SERVICES | ||
| Entity incorporation, state | DE | ||
| Entity tax identification number | 36-2517428 | ||
| Entity address, address line one | 2500 Lake Cook Road | ||
| Entity address, city or town | Riverwoods | ||
| Entity address, state or province | IL | ||
| Entity address, postal zip code | 60015 | ||
| Entity phone number, city area code | 224 | ||
| Entity phone number, local phone number | 405-0900 | ||
| Title of 12(b) security | Common Stock, par value $0.01 per share | ||
| Trading symbol | DFS | ||
| Security exchange name | NYSE | ||
| Entity well-known seasoned issuer | No | ||
| Entity voluntary filers | No | ||
| Entity current reporting status | Yes | ||
| Entity interactive data current | Yes | ||
| Entity filer category | Large Accelerated Filer | ||
| Smaller reporting company | false | ||
| Emerging growth company | false | ||
| ICFR Auditor Attestation Flag | true | ||
| Document Financial Statement Error Correction [Flag] | false | ||
| Entity shell company | false | ||
| Entity public float | $ 32,800,000,000 | ||
| Entity common stock, shares outstanding | 251,605,294 | ||
| Common Stock, par or stated value per share | $ 0.01 | ||
| Central Index Key | 0001393612 | ||
| Current Fiscal Year End Date | --12-31 | ||
| Document Fiscal Year Focus | 2024 | ||
| Document Fiscal Period Focus | FY | ||
| Amendment Flag | true |
