Loans and Leases - Components (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022	Dec. 31, 2021
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases held for investment	$ 83,995	$ 69,001
Allowance for credit losses on loans and leases	(619)	(393)	$ (218)	$ (199)
Total loans and leases held for investment, net	83,376	68,608
Loans held for sale, at fair value	1,926	1,115
Total loans and leases, net	$ 85,302	$ 69,723
Percent of loans held for investment	100.00%	100.00%
Unearned income	$ 243	$ 85
Accrued interest receivable	405	292
Mortgage Loans:
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases held for investment	56,976	54,473
Allowance for credit losses on loans and leases	$ (379)	$ (290)	(208)	(178)
Percent of loans held for investment	67.90%	78.90%
Mortgage Loans: | Multi-family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases held for investment	$ 37,698	$ 38,130
Percent of loans held for investment	44.90%	55.30%
Mortgage Loans: | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases held for investment	$ 10,486	$ 8,526
Percent of loans held for investment	12.50%	12.40%
Mortgage Loans: | One-to-four family first mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases held for investment	$ 5,882	$ 5,821
Percent of loans held for investment	7.00%	8.40%
Mortgage Loans: | Acquisition, development, and construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases held for investment	$ 2,910	$ 1,996
Percent of loans held for investment	3.50%	2.80%
Other Loans:
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases held for investment	$ 27,019	$ 14,528
Allowance for credit losses on loans and leases	$ (240)	$ (103)	$ (10)	$ (21)
Percent of loans held for investment	32.10%	21.10%
Other Loans: | Commercial and industrial loans and lease financing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases held for investment	$ 24,423	$ 12,276
Percent of loans held for investment	29.00%	17.80%
Other Loans: | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases held for investment	$ 21,275	$ 10,597
Percent of loans held for investment	25.30%	15.40%
Other Loans: | Lease financing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases held for investment	$ 3,148	$ 1,679
Percent of loans held for investment	3.70%	2.40%
Other Loans: | Specialty finance loans and leases
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases held for investment	$ 5,200	$ 4,400
Other Loans: | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases held for investment	$ 2,596	$ 2,252
Percent of loans held for investment	3.10%	3.30%