| Document and Entity Information | Dec. 08, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Dec. 8, 2020 |
| Entity Registrant Name | OneMain Holdings, Inc. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-36129 |
| Entity Tax Identification Number | 46-3348401 |
| Entity Address, Address Line One | 601 N.W. SECOND STREET |
| Entity Address, City or Town | EVANSVILLE |
| Entity Address, State or Province | IN |
| Entity Address, Postal Zip Code | 47708 |
| City Area Code | 812 |
| Local Phone Number | 424-8031 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0001584207 |
| Title of 12(b) Security | Common Stock, par value $0.01 per share |
| Trading Symbol | OMF |
| Security Exchange Name | NYSE |
