Investment securities - Additional Information (Detail) $ in Millions	3 Months Ended
Mar. 31, 2026 USD ($) security	Dec. 31, 2025 USD ($)
Investments, Debt and Equity Securities [Abstract]
Number of debt securities with aggregate gross unrealized losses \| security	3,325
Unrealized losses on individual debt securities	$ 925
Cost method equity securities	993
Investment securities pledged to secure debt carrying value	5,800	$ 5,300
Carrying value of investment securities pledged related to repurchase transactions	$ 64	$ 67

Amount of unrealized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), investment in debt security measured at amortized cost (held-to-maturity) and investment in debt security measured at fair value with change in fair value recognized in net income (trading).

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(9)(a))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483621/220-10-S99-2

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(7)(c))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483621/220-10-S99-2

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(3)(d)(2))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477250/944-220-S99-1

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration