v3.26.1
Mortgage Loans Mortgage Loans Held for Sale (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Sep. 30, 2025
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]          
Mortgage loans held for sale $ 2,990.6   $ 2,990.6   $ 2,566.5
Mortgage loans held for sale, outstanding principal amount 3,100.0   3,100.0   2,700.0
Payments for Origination of Mortgage Loans Held-for-sale     17,200.0 $ 17,100.0  
Proceeds from Sale of Mortgage Loans Held-for-sale     16,700.0 16,700.0  
Gain (Loss) on Sales of Loans, Net 142.1 $ 152.8 $ 394.0 $ 423.9  
Loans Sold to FNMA, FHLMC or securities backed by GNMA [Member] | Customer Concentration Risk | Mortgage Loans          
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]          
Concentration Risk, Percentage     74.00%    
Other Customer [Member] | Customer Concentration Risk | Mortgage Loans          
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]          
Concentration Risk, Percentage     18.00%    
Loan Origination Commitments [Member]          
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]          
Derivative, Notional Amount 1,000.0   $ 1,000.0   677.5
Fair Value, Inputs, Level 3 [Member] | Interest rate lock commitments [Member]          
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]          
Derivative, Notional Amount 3,000.0   3,000.0   2,100.0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Loan Origination Commitments [Member]          
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]          
Interest Rate Derivative Instruments Not Designated as Hedging Instruments at Fair Value, Net $ 2.8   $ 2.8   $ 1.9