Goodwill and intangible assets - Intangible Assets by Type (Details) - USD ($) $ in Millions	Jun. 30, 2026	Dec. 31, 2025	Jun. 30, 2025	Dec. 31, 2024
Intangible Assets by Major Class [Line Items]
Gross carrying amount	$ 4,184	$ 4,188
Accumulated amortization	(1,384)	(1,366)
Net carrying amount	2,800	2,822	$ 2,849	$ 2,851
Finite-lived Intangible Assets
Intangible Assets by Major Class [Line Items]
Gross carrying amount	1,598	1,600
Accumulated amortization	(1,384)	(1,366)
Net carrying amount	214	234
Finite-lived Intangible Assets \| Customer contracts—Investment Services \| Securities Services
Intangible Assets by Major Class [Line Items]
Gross carrying amount	730	779
Accumulated amortization	(623)	(616)
Net carrying amount	107	163
Finite-lived Intangible Assets \| Customer contracts—Investment Services \| Market and Wealth Services
Intangible Assets by Major Class [Line Items]
Gross carrying amount	316	269
Accumulated amortization	(273)	(268)
Net carrying amount	43	1
Finite-lived Intangible Assets \| Customer relationships
Intangible Assets by Major Class [Line Items]
Gross carrying amount	512	512
Accumulated amortization	(472)	(467)
Net carrying amount	40	45
Finite-lived Intangible Assets \| Other
Intangible Assets by Major Class [Line Items]
Gross carrying amount	40	40
Accumulated amortization	(16)	(15)
Net carrying amount	24	25
Indefinite-lived Intangible Assets
Intangible Assets by Major Class [Line Items]
Gross carrying amount	2,586	2,588
Net carrying amount	2,586	2,588
Indefinite-lived Intangible Assets \| Tradenames
Intangible Assets by Major Class [Line Items]
Gross carrying amount	1,293	1,294
Net carrying amount	1,293	1,294
Indefinite-lived Intangible Assets \| Customer relationships
Intangible Assets by Major Class [Line Items]
Gross carrying amount	1,293	1,294
Net carrying amount	$ 1,293	$ 1,294