v3.25.2
Fair value measurements - Additional Information (Detail) - USD ($)
3 Months Ended 6 Months Ended
Jun. 30, 2025
Mar. 31, 2025
Jun. 30, 2024
Jun. 30, 2025
Jun. 30, 2024
Dec. 31, 2024
Level 3            
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]            
Change in fair value of nonrecurring fair value measured loans for charge-offs and impairment reserves $ 115,000,000   $ 93,000,000 $ 157,000,000 $ 221,000,000  
Level 3 | Residential Mortgage Loans            
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]            
Capitalized servicing rights, valuation allowance   $ 0   0 0  
Nonrecurring            
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]            
Loans measured at fair value on nonrecurring basis 644,000,000   1,000,000,000.0 644,000,000 1,000,000,000.0 $ 847,000,000
Nonrecurring | Level 2            
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]            
Loans measured at fair value on nonrecurring basis 166,000,000   248,000,000 166,000,000 248,000,000 187,000,000
Nonrecurring | Level 3            
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]            
Loans measured at fair value on nonrecurring basis $ 478,000,000   $ 783,000,000 $ 478,000,000 $ 783,000,000 $ 660,000,000