Other assets - Amortization and Income Tax Credits and Other Income Tax Benefits Related to Tax Credit Investments (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Tax credits and other tax benefits	$ 146	$ 134	$ 282	$ 276
Amortization expense	$ 125	$ 115	$ 247	$ 241

Amount, before amortization expense, of income tax credit and other tax benefit generated by investment under tax credit program elected to be accounted for using proportional amortization method. Includes, but is not limited to, investment under tax credit program not meeting condition for accounting under proportional amortization method.

Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 323
-SubTopic 740
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478156/323-740-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 323
-Name Accounting Standards Codification
-Section 50
-Paragraph 1A
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478156/740-323-50-1A

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration