Fair Value Measures - Carrying Amount and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Carrying Value
Financial Assets:
Cash and cash equivalents	$ 8,484	$ 15,430
FHLB and FRB-NY stock	1,018	1,146
Loans and leases held for investment, net	61,590	67,071
Financial Liabilities:
Deposits	69,152	75,870
Borrowed funds	13,182	14,426
Estimated Fair Value
Financial Assets:
Cash and cash equivalents	8,484	15,430
FHLB and FRB-NY stock	1,018	1,146
Loans and leases held for investment, net	57,767	61,831
Financial Liabilities:
Deposits	69,136	75,894
Borrowed funds	12,965	14,217
Estimated Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial Assets:
Cash and cash equivalents	8,484	15,430
FHLB and FRB-NY stock	0	0
Loans and leases held for investment, net	0	0
Financial Liabilities:
Deposits	46,783	48,546
Borrowed funds	0	0
Estimated Fair Value | Significant Other Observable Inputs (Level 2)
Financial Assets:
Cash and cash equivalents	0	0
FHLB and FRB-NY stock	1,018	1,146
Loans and leases held for investment, net	0	0
Financial Liabilities:
Deposits	22,353	27,348
Borrowed funds	12,965	14,217
Estimated Fair Value | Significant Unobservable Inputs (Level 3)
Financial Assets:
Cash and cash equivalents	0	0
FHLB and FRB-NY stock	0	0
Loans and leases held for investment, net	57,767	61,831
Financial Liabilities:
Deposits	0	0
Borrowed funds	$ 0	$ 0