Fair Value Measures - Carrying Amount and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Carrying Value
Financial Assets:
Cash and cash equivalents	$ 6,929	$ 2,032
FHLB and FRB stock	1,110	1,267
Loans and leases held for investment, net	83,376	68,608
Financial Liabilities:
Deposits	82,675	58,721
Borrowed funds	14,585	21,332
Estimated Fair Value
Financial Assets:
Cash and cash equivalents	6,929	2,032
FHLB and FRB stock	1,110	1,267
Loans and leases held for investment, net	80,331	65,673
Financial Liabilities:
Deposits	82,494	58,479
Borrowed funds	14,317	21,231
Estimated Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial Assets:
Cash and cash equivalents	6,929	2,032
FHLB and FRB stock	0	0
Loans and leases held for investment, net	0	0
Financial Liabilities:
Deposits	65,365	46,211
Borrowed funds	0	0
Estimated Fair Value | Significant Other Observable Inputs (Level 2)
Financial Assets:
Cash and cash equivalents	0	0
FHLB and FRB stock	1,110	1,267
Loans and leases held for investment, net	0	0
Financial Liabilities:
Deposits	17,129	12,268
Borrowed funds	14,317	21,231
Estimated Fair Value | Significant Unobservable Inputs (Level 3)
Financial Assets:
Cash and cash equivalents	0	0
FHLB and FRB stock	0	0
Loans and leases held for investment, net	80,331	65,673
Financial Liabilities:
Deposits	0	0
Borrowed funds	$ 0	$ 0