Goodwill and Other Intangible Assets - Gross Carrying Amount, Accumulated Amortization and Net Carrying Amount of Other Intangible Assets (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023	Dec. 31, 2022
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 3,971	$ 3,938
Accumulated amortization	(2,805)	(2,618)
Net carrying amount	1,166	1,320	$ 1,544
Client relationships
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	2,774	2,761
Accumulated amortization	(1,932)	(1,808)
Net carrying amount	842	953
Technology
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	405	402
Accumulated amortization	(245)	(216)
Net carrying amount	160	186
Core deposits
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	692	690
Accumulated amortization	(543)	(516)
Net carrying amount	149	174
Other
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	100	85
Accumulated amortization	(85)	(78)
Net carrying amount	$ 15	$ 7