Cover Page - shares	9 Months Ended
	Sep. 30, 2019	Nov. 10, 2019
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2019
Document Transition Report	false
Entity File Number	001-36683
Entity Registrant Name	BRIGHTSPHEREInvestment Group Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	47-1121020
Entity Address, Address Line One	200 Clarendon Street, 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
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		86,107,800
Entity Central Index Key	0001748824
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Amendment Flag	false
Common Stock
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