v3.26.1
Current Expected Credit Losses (CECL) - Narrative (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Mar. 31, 2026
Dec. 31, 2025
Mar. 31, 2025
Dec. 31, 2024
Financing Receivable, Allowance for Credit Loss [Line Items]                
Current-period provision for expected credit losses $ 1.1 $ 0.9 $ 1.0 $ 2.0        
Current expected credit losses reserve 25.2 25.2 25.2 25.2 $ 24.1 $ 24.2 $ 28.3 $ 27.2
Accrued commissions and other receivables, net                
Financing Receivable, Allowance for Credit Loss [Line Items]                
Current-period provision for expected credit losses 0.8 0.9 0.9 0.9        
Current expected credit losses reserve 7.1 7.1 7.1 7.1 6.3 6.2 6.2 6.2
Receivables from broker-dealers, clearing organizations, customers and related broker-dealers                
Financing Receivable, Allowance for Credit Loss [Line Items]                
Current-period provision for expected credit losses 0.3 0.0 0.1 1.1        
Current expected credit losses reserve $ 18.1 18.1 $ 18.1 18.1 $ 17.8 $ 18.0 $ 22.1 $ 21.0
Allowance for credit losses, period increase (decrease)   $ (4.0)   $ (2.9)