| Cover Page | Mar. 30, 2021 |
| Entity Information [Line Items] | |
| Document Type | 8-K |
| Document Period End Date | Mar. 30, 2021 |
| Entity Registrant Name | BrightSphere Investment Group Inc. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-36683 |
| Entity Tax Identification Number | 47-1121020 |
| Entity Address, Address Line One | 200 Clarendon Street |
| Entity Address, Address Line Two | 53rd Floor |
| Entity Address, City or Town | Boston |
| Entity Address, State or Province | MA |
| Entity Address, Postal Zip Code | 02116 |
| City Area Code | 617 |
| Local Phone Number | 369-7300 |
| 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 | 0001748824 |
| Amendment Flag | false |
| Common stock, par value $0.001 per share | |
| Entity Information [Line Items] | |
| Title of 12(b) Security | Common stock, par value $0.001 per share |
| Trading Symbol | BSIG |
| Security Exchange Name | NYSE |
| 4.800% Notes due 2026 | |
| Entity Information [Line Items] | |
| Title of 12(b) Security | 4.800% Notes due 2026 |
| Trading Symbol | BSIG 26 |
| Security Exchange Name | NYSE |
| 5.125% Notes due 2031 | |
| Entity Information [Line Items] | |
| Title of 12(b) Security | 5.125% Notes due 2031 |
| Trading Symbol | BSA |
| Security Exchange Name | NYSE |
