v3.22.1
BORROWINGS (Details)
3 Months Ended 12 Months Ended
Mar. 31, 2022
USD ($)
Institution
Dec. 31, 2021
USD ($)
Dec. 31, 2017
USD ($)
Debt Instrument [Line Items]      
Long-term line of credit $ 0    
Loans pledged as collateral 4,400,000,000    
Federal Home Loan Bank, maximum borrowing capacity 2,800,000,000    
Federal Home Loan Bank, additional credit available 278,000,000    
Unsecured debt $ 245,000,000    
Number of financial institutions | Institution 5    
Unused lines of credit $ 3,200,000,000 $ 3,100,000,000  
FHLB Advances Maturing in October 2020      
Debt Instrument [Line Items]      
Secured debt   148,000,000  
Minimum      
Debt Instrument [Line Items]      
Unsecured debt 20,000,000    
Maximum      
Debt Instrument [Line Items]      
Unsecured debt 100,000,000    
Revolving Credit Facility      
Debt Instrument [Line Items]      
Line of credit, borrowing capacity     $ 20,000,000
Revolving Credit Facility | 90 Day LIBOR      
Debt Instrument [Line Items]      
Debt instrument basis point rate     0.50%
U.S. Treasury      
Debt Instrument [Line Items]      
Securities pledged as collateral 900,000    
Subordinated Notes Due 2030      
Debt Instrument [Line Items]      
Subordinated notes $ 173,000,000 26,000,000  
Line of credit facility, Interest rate 6.00%    
Interest rate (as a percent) 3.50%    
Secured debt $ 153,000,000 $ 166,000,000  
Subordinated Notes Due 2030 | Secured Overnight Financing Rate (SOFR)      
Debt Instrument [Line Items]      
Debt instrument basis point rate 2.04% 5.90%  
Subordinated Notes Due 2032      
Debt Instrument [Line Items]      
Subordinated notes $ 150,000,000    
FFI      
Debt Instrument [Line Items]      
Long-term line of credit   $ 18,500,000  
FFI | Subordinated Notes Due 2030      
Debt Instrument [Line Items]      
Subordinated notes $ 23,000,000