Fair value measurement - Schedule of Corporation’s Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2026	Dec. 31, 2025
Assets
Debt securities available-for-sale:	$ 24,792,834	$ 20,574,972
Mortgage servicing rights	94,485	96,356
U.S. Treasury securities
Assets
Debt securities available-for-sale:	20,270,608	15,723,454
Collateralized mortgage obligations - federal agencies
Assets
Debt securities available-for-sale:	89,533	100,241
Other
Assets
Debt securities available-for-sale:	521	750
Recurring
Assets
Debt securities available-for-sale:	24,792,834	20,574,972
Trading account debt securities, excluding derivatives:	31,171	36,569
Equity securities	57,420	51,484
Mortgage servicing rights	94,485	96,356
Loans held-for-sale	4,879	9,998
Derivatives	28,518	27,913
Total assets measured at fair value on a recurring basis	25,009,307	20,797,292
Liabilities
Derivatives	(26,953)	(25,740)
Total liabilities measured at fair value on a recurring basis	(26,953)	(25,740)
Recurring | U.S. Treasury securities
Assets
Debt securities available-for-sale:	20,270,608	15,723,454
Trading account debt securities, excluding derivatives:	3,754	12,460
Recurring | Obligations of Puerto Rico, States and political subdivisions
Assets
Trading account debt securities, excluding derivatives:	45	45
Recurring | Collateralized mortgage obligations - federal agencies
Assets
Debt securities available-for-sale:	89,533	100,241
Recurring | Collateralized mortgage obligations
Assets
Trading account debt securities, excluding derivatives:	514	567
Recurring | Mortgage-backed securities - federal agencies
Assets
Debt securities available-for-sale:	4,432,172	4,750,527
Trading account debt securities, excluding derivatives:	26,769	23,398
Recurring | Other
Assets
Debt securities available-for-sale:	521	750
Trading account debt securities, excluding derivatives:	89	99
Recurring | Level 1
Assets
Debt securities available-for-sale:	10,040,663	6,576,313
Trading account debt securities, excluding derivatives:	3,405	12,450
Equity securities	0	0
Mortgage servicing rights	0	0
Loans held-for-sale	0	0
Derivatives	0	0
Total assets measured at fair value on a recurring basis	10,044,068	6,588,763
Liabilities
Derivatives	0	0
Total liabilities measured at fair value on a recurring basis	0	0
Recurring | Level 1 | U.S. Treasury securities
Assets
Debt securities available-for-sale:	10,040,663	6,576,313
Trading account debt securities, excluding derivatives:	3,405	12,450
Recurring | Level 1 | Obligations of Puerto Rico, States and political subdivisions
Assets
Trading account debt securities, excluding derivatives:	0	0
Recurring | Level 1 | Collateralized mortgage obligations - federal agencies
Assets
Debt securities available-for-sale:	0	0
Recurring | Level 1 | Collateralized mortgage obligations
Assets
Trading account debt securities, excluding derivatives:	0	0
Recurring | Level 1 | Mortgage-backed securities - federal agencies
Assets
Debt securities available-for-sale:	0	0
Trading account debt securities, excluding derivatives:	0	0
Recurring | Level 1 | Other
Assets
Debt securities available-for-sale:	0	0
Trading account debt securities, excluding derivatives:	0	0
Recurring | Level 2
Assets
Debt securities available-for-sale:	14,751,293	13,997,504
Trading account debt securities, excluding derivatives:	27,592	23,936
Equity securities	56,034	50,632
Mortgage servicing rights	0	0
Loans held-for-sale	4,879	9,998
Derivatives	28,518	27,913
Total assets measured at fair value on a recurring basis	14,868,316	14,109,983
Liabilities
Derivatives	(26,953)	(25,740)
Total liabilities measured at fair value on a recurring basis	(26,953)	(25,740)
Recurring | Level 2 | U.S. Treasury securities
Assets
Debt securities available-for-sale:	10,229,945	9,147,141
Trading account debt securities, excluding derivatives:	349	10
Recurring | Level 2 | Obligations of Puerto Rico, States and political subdivisions
Assets
Trading account debt securities, excluding derivatives:	45	45
Recurring | Level 2 | Collateralized mortgage obligations - federal agencies
Assets
Debt securities available-for-sale:	89,533	100,241
Recurring | Level 2 | Collateralized mortgage obligations
Assets
Trading account debt securities, excluding derivatives:	514	567
Recurring | Level 2 | Mortgage-backed securities - federal agencies
Assets
Debt securities available-for-sale:	4,431,815	4,750,122
Trading account debt securities, excluding derivatives:	26,684	23,314
Recurring | Level 2 | Other
Assets
Debt securities available-for-sale:	0	0
Trading account debt securities, excluding derivatives:	0	0
Recurring | Level 3
Assets
Debt securities available-for-sale:	878	1,155
Trading account debt securities, excluding derivatives:	174	183
Equity securities	0	0
Mortgage servicing rights	94,485	96,356
Loans held-for-sale	0	0
Derivatives	0	0
Total assets measured at fair value on a recurring basis	95,537	97,694
Liabilities
Derivatives	0	0
Total liabilities measured at fair value on a recurring basis	0	0
Recurring | Level 3 | U.S. Treasury securities
Assets
Debt securities available-for-sale:	0	0
Trading account debt securities, excluding derivatives:	0	0
Recurring | Level 3 | Obligations of Puerto Rico, States and political subdivisions
Assets
Trading account debt securities, excluding derivatives:	0	0
Recurring | Level 3 | Collateralized mortgage obligations - federal agencies
Assets
Debt securities available-for-sale:	0	0
Recurring | Level 3 | Collateralized mortgage obligations
Assets
Trading account debt securities, excluding derivatives:	0	0
Recurring | Level 3 | Mortgage-backed securities - federal agencies
Assets
Debt securities available-for-sale:	357	405
Trading account debt securities, excluding derivatives:	85	84
Recurring | Level 3 | Other
Assets
Debt securities available-for-sale:	521	750
Trading account debt securities, excluding derivatives:	89	99
Recurring | Measured at NAV
Assets
Debt securities available-for-sale:	0	0
Trading account debt securities, excluding derivatives:	0	0
Equity securities	1,386	852
Mortgage servicing rights	0	0
Loans held-for-sale	0	0
Derivatives	0	0
Total assets measured at fair value on a recurring basis	1,386	852
Liabilities
Derivatives	0	0
Total liabilities measured at fair value on a recurring basis	0	0
Recurring | Measured at NAV | U.S. Treasury securities
Assets
Debt securities available-for-sale:	0	0
Trading account debt securities, excluding derivatives:	0	0
Recurring | Measured at NAV | Obligations of Puerto Rico, States and political subdivisions
Assets
Trading account debt securities, excluding derivatives:	0	0
Recurring | Measured at NAV | Collateralized mortgage obligations - federal agencies
Assets
Debt securities available-for-sale:	0	0
Recurring | Measured at NAV | Collateralized mortgage obligations
Assets
Trading account debt securities, excluding derivatives:	0	0
Recurring | Measured at NAV | Mortgage-backed securities - federal agencies
Assets
Debt securities available-for-sale:	0	0
Trading account debt securities, excluding derivatives:	0	0
Recurring | Measured at NAV | Other
Assets
Debt securities available-for-sale:	0	0
Trading account debt securities, excluding derivatives:	$ 0	$ 0