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Loans and ACL - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
Loans and ACL - Narrative (Details) - USD ($) $ in Millions	Sep. 30, 2026	Sep. 30, 2026	Sep. 30, 2026	Sep. 30, 2025
Financing Receivable
Trial modifications			$ 157	$ 72
Unfunded lending commitments related to the modified obligations	$ 387	$ 387	387	$ 584
Commercial:
Financing Receivable
Allowance increase (decrease)	(103)	(138)
Consumer:
Financing Receivable
Allowance increase (decrease)	(817)	(829)
Indirect auto
Financing Receivable
Value of loans being sold	5,500	$ 5,500	$ 5,500
Proceeds from sale of loan	5,200
Credit loss, reversal	$ 581