Loans and Leases - Components (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases held for investment	$ 84,619	$ 69,001
Allowance for credit losses on loans and leases	(992)	(393)	$ (199)
Total loans and leases held for investment, net	83,627	68,608
Loans held for sale ($902 and $1,115 measured at fair value, respectively)	1,182	1,115
Total loans and leases, net	$ 84,809	$ 69,723
Percent of loans held for investment	100.00%	100.00%
Unearned income	$ 258	$ 85
Accrued interest receivable	$ 423	$ 292
Financing Receivable, Accrued Interest, after Allowance for Credit Loss, Statement of Financial Position [Extensible Enumeration]	Other assets	Other assets
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases held for investment	$ 27,911	$ 14,528
Percent of loans held for investment	33.00%	21.10%
Mortgage Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases held for investment	$ 56,708	$ 54,473
Allowance for credit losses on loans and leases	$ (756)	$ (290)	(178)
Percent of loans held for investment	67.00%	78.90%
Mortgage Loans | Multi-family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases held for investment	$ 37,265	$ 38,130
Percent of loans held for investment	44.00%	55.30%
Mortgage Loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases held for investment	$ 10,470	$ 8,526
Percent of loans held for investment	12.40%	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	$ 6,061	$ 5,821
Percent of loans held for investment	7.20%	8.40%
Mortgage Loans | Acquisition, development, and construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases held for investment	$ 2,912	$ 1,996
Percent of loans held for investment	3.40%	2.80%
Other Loans:
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases held for investment	$ 27,911	$ 14,528
Allowance for credit losses on loans and leases	(236)	(103)	$ (21)
Other Loans: | Commercial and industrial loans and lease financing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases held for investment	$ 25,254	$ 12,276
Percent of loans held for investment	29.90%	17.80%
Other Loans: | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases held for investment	$ 22,065	$ 10,597
Percent of loans held for investment	26.10%	15.40%
Other Loans: | Lease financing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases held for investment	$ 3,189	$ 1,679
Percent of loans held for investment	3.80%	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	$ 2,657	$ 2,252
Percent of loans held for investment	3.10%	3.30%