v3.25.3
Fair Value Measurements (Details) - USD ($)
$ in Millions
9 Months Ended
Sep. 30, 2025
Dec. 31, 2024
Asset of BSIF and consolidated Funds    
Total fair value assets $ 222.5 $ 221.9
Uncategorized 3.4 19.4
Liabilities of consolidated Funds    
Total fair value liabilities $ (32.3) (20.7)
Real estate investment funds    
Liabilities of consolidated Funds    
Term over which the underlying assets are expected to be liquidated by the investees 1 year  
Quoted prices in active markets (Level I)    
Asset of BSIF and consolidated Funds    
Total fair value assets $ 148.7 142.7
Liabilities of consolidated Funds    
Total fair value liabilities (26.0) (20.4)
Significant other observable inputs (Level II)    
Asset of BSIF and consolidated Funds    
Total fair value assets 70.4 59.8
Liabilities of consolidated Funds    
Total fair value liabilities (6.3) (0.3)
Significant unobservable inputs (Level III)    
Asset of BSIF and consolidated Funds    
Total fair value assets 0.0 0.0
Liabilities of consolidated Funds    
Total fair value liabilities 0.0 0.0
Consolidated Funds    
Asset of BSIF and consolidated Funds    
Common and preferred stock 111.2 94.2
Derivatives 6.2 0.7
Investments in unconsolidated Funds 181.7 154.0
Liabilities of consolidated Funds    
Securities sold short (26.0) (20.4)
Derivatives (6.3) (0.3)
Consolidated Funds | Corporate bonds    
Asset of BSIF and consolidated Funds    
Corporate bonds 64.3 59.1
Consolidated Funds | Quoted prices in active markets (Level I)    
Asset of BSIF and consolidated Funds    
Common and preferred stock 111.2 94.2
Derivatives 0.1 0.0
Liabilities of consolidated Funds    
Securities sold short (26.0) (20.4)
Derivatives 0.0 0.0
Consolidated Funds | Quoted prices in active markets (Level I) | Corporate bonds    
Asset of BSIF and consolidated Funds    
Corporate bonds 0.0 0.0
Consolidated Funds | Significant other observable inputs (Level II)    
Asset of BSIF and consolidated Funds    
Common and preferred stock 0.0 0.0
Derivatives 6.1 0.7
Liabilities of consolidated Funds    
Securities sold short 0.0 0.0
Derivatives (6.3) (0.3)
Consolidated Funds | Significant other observable inputs (Level II) | Corporate bonds    
Asset of BSIF and consolidated Funds    
Corporate bonds 64.3 59.1
Consolidated Funds | Significant unobservable inputs (Level III)    
Asset of BSIF and consolidated Funds    
Common and preferred stock 0.0 0.0
Derivatives 0.0 0.0
Liabilities of consolidated Funds    
Securities sold short 0.0 0.0
Derivatives 0.0 0.0
Consolidated Funds | Significant unobservable inputs (Level III) | Corporate bonds    
Asset of BSIF and consolidated Funds    
Corporate bonds 0.0 0.0
Consolidated Entity Excluding Consolidated Funds    
Asset of BSIF and consolidated Funds    
Consolidated Funds total 181.7 154.0
AAMI total 40.8 67.9
Uncategorized 3.4 19.4
Liabilities of consolidated Funds    
Consolidated Funds total (32.3) (20.7)
Consolidated Entity Excluding Consolidated Funds | Investments related to long-term incentive compensation plans    
Asset of BSIF and consolidated Funds    
Investments related to long-term incentive compensation plans 37.4 48.5
Investments in unconsolidated Funds 37.4 48.5
Consolidated Entity Excluding Consolidated Funds | Investments in unconsolidated Funds    
Asset of BSIF and consolidated Funds    
Investments in unconsolidated Funds 3.4 19.4
Uncategorized 3.4 19.4
Consolidated Entity Excluding Consolidated Funds | Investment funds subject to longer redemption restrictions    
Asset of BSIF and consolidated Funds    
Uncategorized 3.2 2.9
Consolidated Entity Excluding Consolidated Funds | Quoted prices in active markets (Level I)    
Asset of BSIF and consolidated Funds    
Consolidated Funds total 111.3 94.2
AAMI total 37.4 48.5
Liabilities of consolidated Funds    
Consolidated Funds total (26.0) (20.4)
Consolidated Entity Excluding Consolidated Funds | Quoted prices in active markets (Level I) | Investments related to long-term incentive compensation plans    
Asset of BSIF and consolidated Funds    
Investments related to long-term incentive compensation plans 37.4 48.5
Consolidated Entity Excluding Consolidated Funds | Quoted prices in active markets (Level I) | Investments in unconsolidated Funds    
Asset of BSIF and consolidated Funds    
Investments in unconsolidated Funds 0.0 0.0
Consolidated Entity Excluding Consolidated Funds | Significant other observable inputs (Level II)    
Asset of BSIF and consolidated Funds    
Consolidated Funds total 70.4 59.8
AAMI total 0.0 0.0
Liabilities of consolidated Funds    
Consolidated Funds total (6.3) (0.3)
Consolidated Entity Excluding Consolidated Funds | Significant other observable inputs (Level II) | Investments related to long-term incentive compensation plans    
Asset of BSIF and consolidated Funds    
Investments related to long-term incentive compensation plans 0.0 0.0
Consolidated Entity Excluding Consolidated Funds | Significant other observable inputs (Level II) | Investments in unconsolidated Funds    
Asset of BSIF and consolidated Funds    
Investments in unconsolidated Funds 0.0 0.0
Consolidated Entity Excluding Consolidated Funds | Significant unobservable inputs (Level III)    
Asset of BSIF and consolidated Funds    
Consolidated Funds total 0.0 0.0
AAMI total 0.0 0.0
Liabilities of consolidated Funds    
Consolidated Funds total 0.0 0.0
Consolidated Entity Excluding Consolidated Funds | Significant unobservable inputs (Level III) | Investments related to long-term incentive compensation plans    
Asset of BSIF and consolidated Funds    
Investments related to long-term incentive compensation plans 0.0 0.0
Consolidated Entity Excluding Consolidated Funds | Significant unobservable inputs (Level III) | Investments in unconsolidated Funds    
Asset of BSIF and consolidated Funds    
Investments in unconsolidated Funds $ 0.0 $ 0.0