v3.26.1
Fair Value (Reconciliation of Recurring Fair Value Measurements) (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Unrealized gains/losses for the period on assets held on Consolidated Balance Sheet
Fair Value, Recurring | Level 3    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance 7,679 7,431
Included in Earnings 24 11
Included in other comprehensive income (3) 8
Purchases 295 254
Sales (227) (110)
Issuances 25 16
Settlements (193) (188)
Transfers into Level 3 2 4
Transfers out of Level 3 (11) (5)
Ending balance 7,601 7,421
Unrealized gains/losses for the period on assets held on Consolidated Balance Sheet 11 (13)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance 223 337
Included in Earnings 20 47
Included in other comprehensive income 0 0
Purchases 0 0
Sales 8 0
Issuances 217 5
Settlements (291) (86)
Transfers into Level 3 0 0
Transfers out of Level 3 0 0
Ending balance 177 303
Unrealized gains/losses for the period on liabilities held on Consolidated Balance Sheet 31 45
Fair Value Additional Information [Abstract]    
Net gains (losses) included in earnings (realized and unrealized) relating to Level 3 assets and liabilities 4 (36)
Net unrealized gains (losses) relating to Level 3 assets and liabilities (20) (58)
Fair Value, Recurring | Level 3 | FirstBank Holding Company    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Purchases 10  
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Purchases 0  
Fair Value, Recurring | Level 3 | Other borrowed funds    
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance 7 10
Included in Earnings 0 0
Included in other comprehensive income 0 0
Purchases 0 0
Sales 0 0
Issuances 3 5
Settlements (5) (2)
Transfers into Level 3 0 0
Transfers out of Level 3 0 0
Ending balance 5 13
Unrealized gains/losses for the period on liabilities held on Consolidated Balance Sheet 0 0
Fair Value, Recurring | Level 3 | Other borrowed funds | FirstBank Holding Company    
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Purchases 0  
Fair Value, Recurring | Level 3 | Financial derivatives    
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance 79 150
Included in Earnings 25 37
Included in other comprehensive income 0 0
Purchases 0 0
Sales 8 0
Issuances 0 0
Settlements (77) (26)
Transfers into Level 3 0 0
Transfers out of Level 3 0 0
Ending balance 35 161
Unrealized gains/losses for the period on liabilities held on Consolidated Balance Sheet 32 38
Fair Value, Recurring | Level 3 | Financial derivatives | FirstBank Holding Company    
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Purchases 0  
Fair Value, Recurring | Level 3 | Other liabilities    
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance 137 177
Included in Earnings (5) 10
Included in other comprehensive income 0 0
Purchases 0 0
Sales 0 0
Issuances 214 0
Settlements (209) (58)
Transfers into Level 3 0 0
Transfers out of Level 3 0 0
Ending balance 137 129
Unrealized gains/losses for the period on liabilities held on Consolidated Balance Sheet (1) 7
Fair Value, Recurring | Level 3 | Other liabilities | FirstBank Holding Company    
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Purchases 0  
Loans held for sale | Fair Value, Recurring | Level 3 | Residential mortgage loans held for sale    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance 108 68
Included in Earnings 0 0
Included in other comprehensive income 0 0
Purchases 0 41
Sales (33) 0
Issuances 0 0
Settlements (2) (4)
Transfers into Level 3 2 4
Transfers out of Level 3 (1) (5)
Ending balance 74 104
Unrealized gains/losses for the period on assets held on Consolidated Balance Sheet 0 0
Loans held for sale | Fair Value, Recurring | Level 3 | Residential mortgage loans held for sale | FirstBank Holding Company    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Purchases 0  
Loans held for sale | Fair Value, Recurring | Level 3 | Commercial mortgage loans held for sale    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance   4
Included in Earnings   0
Included in other comprehensive income   0
Purchases   0
Sales   0
Issuances   0
Settlements   0
Transfers into Level 3   0
Transfers out of Level 3   0
Ending balance   4
Unrealized gains/losses for the period on assets held on Consolidated Balance Sheet   0
Securities available-for-sale | Fair Value, Recurring | Level 3    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance 769 853
Included in Earnings 4 0
Included in other comprehensive income (3) 8
Purchases 0 0
Sales 0 0
Issuances 0 0
Settlements (19) (20)
Transfers into Level 3 0 0
Transfers out of Level 3 0 0
Ending balance 751 841
Unrealized gains/losses for the period on assets held on Consolidated Balance Sheet 0 (3)
Securities available-for-sale | Fair Value, Recurring | Level 3 | FirstBank Holding Company    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Purchases 0  
Residential mortgage- backed non-agency | Fair Value, Recurring | Level 3    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance 548 603
Included in Earnings 3 2
Included in other comprehensive income (3) 8
Purchases 0 0
Sales 0 0
Issuances 0 0
Settlements (15) (17)
Transfers into Level 3 0 0
Transfers out of Level 3 0 0
Ending balance 533 596
Unrealized gains/losses for the period on assets held on Consolidated Balance Sheet 0 0
Residential mortgage- backed non-agency | Fair Value, Recurring | Level 3 | FirstBank Holding Company    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Purchases 0  
Commercial mortgage- backed non-agency | Fair Value, Recurring | Level 3    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance 79 103
Included in Earnings 0 (3)
Included in other comprehensive income 0 (1)
Purchases 0 0
Sales 0 0
Issuances 0 0
Settlements 0 0
Transfers into Level 3 0 0
Transfers out of Level 3 0 0
Ending balance 79 99
Unrealized gains/losses for the period on assets held on Consolidated Balance Sheet 0 (3)
Commercial mortgage- backed non-agency | Fair Value, Recurring | Level 3 | FirstBank Holding Company    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Purchases 0  
Asset-backed | Fair Value, Recurring | Level 3    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance 87 93
Included in Earnings 0 1
Included in other comprehensive income 0 1
Purchases 0 0
Sales 0 0
Issuances 0 0
Settlements (3) (3)
Transfers into Level 3 0 0
Transfers out of Level 3 0 0
Ending balance 84 92
Unrealized gains/losses for the period on assets held on Consolidated Balance Sheet 0 0
Asset-backed | Fair Value, Recurring | Level 3 | FirstBank Holding Company    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Purchases 0  
Other | Fair Value, Recurring | Level 3    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance 55 54
Included in Earnings 1 0
Included in other comprehensive income 0 0
Purchases 0 0
Sales 0 0
Issuances 0 0
Settlements (1) 0
Transfers into Level 3 0 0
Transfers out of Level 3 0 0
Ending balance 55 54
Unrealized gains/losses for the period on assets held on Consolidated Balance Sheet 0 0
Other | Fair Value, Recurring | Level 3 | FirstBank Holding Company    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Purchases 0  
Loans | Fair Value, Recurring | Level 3    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance 620 670
Included in Earnings 2 5
Included in other comprehensive income 0 0
Purchases 6 7
Sales 0 0
Issuances 0 0
Settlements (19) (19)
Transfers into Level 3 0 0
Transfers out of Level 3 (10) 0
Ending balance 599 663
Unrealized gains/losses for the period on assets held on Consolidated Balance Sheet 2 5
Loans | Fair Value, Recurring | Level 3 | FirstBank Holding Company    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Purchases 0  
Equity investments | Fair Value, Recurring | Level 3    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance 2,503 2,111
Included in Earnings (26) 46
Included in other comprehensive income 0 0
Purchases 58 176
Sales (194) (110)
Issuances 0 0
Settlements 0 0
Transfers into Level 3 0 0
Transfers out of Level 3 0 0
Ending balance 2,341 2,223
Unrealized gains/losses for the period on assets held on Consolidated Balance Sheet (36) 25
Equity investments | Fair Value, Recurring | Level 3 | FirstBank Holding Company    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Purchases 0  
Mortgage Servicing Rights | Fair Value, Recurring | Level 3 | Residential mortgage loans held for sale    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance 2,638 2,626
Included in Earnings (13) (51)
Included in other comprehensive income 0 0
Purchases 214 1
Sales 0 0
Issuances 10 7
Settlements (73) (60)
Transfers into Level 3 0 0
Transfers out of Level 3 0 0
Ending balance 2,786 2,523
Unrealized gains/losses for the period on assets held on Consolidated Balance Sheet (13) (51)
Mortgage Servicing Rights | Fair Value, Recurring | Level 3 | Residential mortgage loans held for sale | FirstBank Holding Company    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Purchases 10  
Mortgage Servicing Rights | Fair Value, Recurring | Level 3 | Commercial mortgage loans held for sale    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance 1,021 1,085
Included in Earnings 49 (2)
Included in other comprehensive income 0 0
Purchases 16 27
Sales 0 0
Issuances 15 9
Settlements (71) (78)
Transfers into Level 3 0 0
Transfers out of Level 3 0 0
Ending balance 1,030 1,041
Unrealized gains/losses for the period on assets held on Consolidated Balance Sheet 49 (2)
Mortgage Servicing Rights | Fair Value, Recurring | Level 3 | Commercial mortgage loans held for sale | FirstBank Holding Company    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Purchases 0  
Financial derivatives | Fair Value, Recurring | Level 3    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance 6 4
Included in Earnings 8 13
Included in other comprehensive income 0 0
Purchases 0 0
Sales 0 0
Issuances 0 0
Settlements (9) (7)
Transfers into Level 3 0 0
Transfers out of Level 3 0 0
Ending balance 5 10
Unrealized gains/losses for the period on assets held on Consolidated Balance Sheet 9 13
Financial derivatives | Fair Value, Recurring | Level 3 | FirstBank Holding Company    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Purchases 0  
Other assets | Fair Value, Recurring | Level 3    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance 14 10
Included in Earnings 0 0
Included in other comprehensive income 0 0
Purchases 1 2
Sales 0 0
Issuances 0 0
Settlements 0 0
Transfers into Level 3 0 0
Transfers out of Level 3 0 0
Ending balance 15 12
Unrealized gains/losses for the period on assets held on Consolidated Balance Sheet 0 $ 0
Other assets | Fair Value, Recurring | Level 3 | FirstBank Holding Company    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Purchases $ 0