Loans - Wholesale Loan Portfolio, Payment Status of FDMs (Details) - Wholesale - USD ($) $ in Millions	Sep. 30, 2026	Sep. 30, 2025
Secured by real estate
Financing Receivable, Modified [Line Items]
Amortized cost of FDMs during the last 12 months	$ 647	$ 783
Secured by real estate \| Criticized nonaccrual
Financing Receivable, Modified [Line Items]
Amortized cost of FDMs during the last 12 months	161	375
Secured by real estate \| Current and less than 30 days past due and still accruing
Financing Receivable, Modified [Line Items]
Amortized cost of FDMs during the last 12 months	445	408
Secured by real estate \| 30–89 days past due and still accruing
Financing Receivable, Modified [Line Items]
Amortized cost of FDMs during the last 12 months	1	0
Secured by real estate \| 90 or more days past due and still accruing
Financing Receivable, Modified [Line Items]
Amortized cost of FDMs during the last 12 months	40	0
Commercial and industrial
Financing Receivable, Modified [Line Items]
Amortized cost of FDMs during the last 12 months	1,985	2,506
Commercial and industrial \| Criticized nonaccrual
Financing Receivable, Modified [Line Items]
Amortized cost of FDMs during the last 12 months	654	800
Commercial and industrial \| Current and less than 30 days past due and still accruing
Financing Receivable, Modified [Line Items]
Amortized cost of FDMs during the last 12 months	1,306	1,683
Commercial and industrial \| 30–89 days past due and still accruing
Financing Receivable, Modified [Line Items]
Amortized cost of FDMs during the last 12 months	25	10
Commercial and industrial \| 90 or more days past due and still accruing
Financing Receivable, Modified [Line Items]
Amortized cost of FDMs during the last 12 months	0	13
Other
Financing Receivable, Modified [Line Items]
Amortized cost of FDMs during the last 12 months	243	91
Other \| Criticized nonaccrual
Financing Receivable, Modified [Line Items]
Amortized cost of FDMs during the last 12 months	92	12
Other \| Current and less than 30 days past due and still accruing
Financing Receivable, Modified [Line Items]
Amortized cost of FDMs during the last 12 months	151	79
Other \| 30–89 days past due and still accruing
Financing Receivable, Modified [Line Items]
Amortized cost of FDMs during the last 12 months	0	0
Other \| 90 or more days past due and still accruing
Financing Receivable, Modified [Line Items]
Amortized cost of FDMs during the last 12 months	$ 0	$ 0