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Borrowings (Narrative) (Details) - USD ($)	1 Months Ended	6 Months Ended
Borrowings (Narrative) (Details) - USD ($)	Sep. 30, 2026	Mar. 31, 2027	Dec. 31, 2025
Federal Home Loan Bank, Advance, Branch of FHLBank [Line Items]
FHLB advances	$ 3,300,000,000		$ 3,200,000,000
Subordinated Debt	696,000,000		$ 435,000,000
Other Subordinated Debt \| Subordinated Notes Due In 2036
Federal Home Loan Bank, Advance, Branch of FHLBank [Line Items]
Issued amount	$ 250,000,000
Interest rate	6.721%
Debt instrument, basis spread on variable rate	1.95%
Debt instrument, term	5 years
Debt issuance cost	$ 4,000,000
Long-term debt	$ 246,000,000
Junior Subordinated Debt \| Expected
Federal Home Loan Bank, Advance, Branch of FHLBank [Line Items]
Redemption amount		$ 240,000,000
Minimum
Federal Home Loan Bank, Advance, Branch of FHLBank [Line Items]
FHLB advances fixed interest rate	3.95%
Maximum
Federal Home Loan Bank, Advance, Branch of FHLBank [Line Items]
FHLB advances fixed interest rate	4.37%