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Business Segments - Narrative (Details) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
Business Segments - Narrative (Details) $ in Millions	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2024 USD ($) segment	Sep. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Segment Reporting Information
Number of business segments \| segment			3
Other noninterest expense	$ (245)	$ (238)	$ (768)	$ (756)
Wealth and asset management revenue	(163)	(145)	(483)	(434)
Operating Segments \| Investment Advisors [Member]
Segment Reporting Information
Other noninterest expense	(38)	(34)	(112)	(105)
Wealth and asset management revenue	$ (98)	$ (92)	$ (296)	$ (273)
Operating Segments \| Investment Advisors [Member] \| Revision of Prior Period, Adjustment
Segment Reporting Information
Other noninterest expense					$ 186	$ 177	$ 180
Wealth and asset management revenue					$ 186	$ 177	$ 180