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Loans and Leases - Performance of Loans Modified in Last 12 Months (Details) - USD ($) $ in Millions | Sep. 30, 2025 | Sep. 30, 2024
--- | --- | ---
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Total | $ 29 | $ 58
Current |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Total | 3 | 42
30 - 89 Past Due |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Total | 6 | 2
90+ Past Due |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Total | 20 | 14
Loans and leases held for investment: | Multi-family |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Total |  | 24
Loans and leases held for investment: | Multi-family | Current |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Total |  | 24
Loans and leases held for investment: | Multi-family | 30 - 89 Past Due |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Total |  | 0
Loans and leases held for investment: | Multi-family | 90+ Past Due |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Total |  | 0
Loans and leases held for investment: | Commercial real estate |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Total | 6 | 12
Loans and leases held for investment: | Commercial real estate | Current |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Total | 0 | 8
Loans and leases held for investment: | Commercial real estate | 30 - 89 Past Due |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Total | 6 | 0
Loans and leases held for investment: | Commercial real estate | 90+ Past Due |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Total | 0 | 4
Loans and leases held for investment: | One-to-four family first mortgage |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Total | 23 | 12
Loans and leases held for investment: | One-to-four family first mortgage | Current |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Total | 3 | 7
Loans and leases held for investment: | One-to-four family first mortgage | 30 - 89 Past Due |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Total | 0 | 0
Loans and leases held for investment: | One-to-four family first mortgage | 90+ Past Due |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Total | $ 20 | 5
Other loans held for investment | Commercial and Industrial |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Total |  | 9
Other loans held for investment | Commercial and Industrial | Current |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Total |  | 2
Other loans held for investment | Commercial and Industrial | 30 - 89 Past Due |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Total |  | 2
Other loans held for investment | Commercial and Industrial | 90+ Past Due |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Total |  | 5
Other loans held for investment | Other |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Total |  | 1
Other loans held for investment | Other | Current |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Total |  | 1
Other loans held for investment | Other | 30 - 89 Past Due |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Total |  | 0
Other loans held for investment | Other | 90+ Past Due |  |
Financing Receivable, Troubled Debt Restructuring [Line Items] |  |
Total |  | $ 0

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