Goodwill and Other Intangible Assets - Gross Carrying Amount, Accumulated Amortization and Net Carrying Amount of Other Intangible Assets (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 3,887	$ 3,897
Accumulated amortization	(2,524)	(2,353)
Net carrying amount	1,363	1,544	$ 1,816
Client relationships
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	2,722	2,728
Accumulated amortization	(1,743)	(1,626)
Net carrying amount	979	1,102
Technology
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	401	402
Accumulated amortization	(206)	(178)
Net carrying amount	195	224
Core deposits
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	681	683
Accumulated amortization	(501)	(477)
Net carrying amount	180	206
Other
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	83	84
Accumulated amortization	(74)	(72)
Net carrying amount	$ 9	$ 12