Borrowings - FHLB Advances - Additional Information (Details)	12 Months Ended
	Dec. 31, 2023 USD ($) Loan	Dec. 31, 2022 USD ($) Loan	Dec. 31, 2021 USD ($)
Debt Instrument [Line Items]
Weighted-average cost related to FHLB advances (in hundredths)	5.54%	4.58%
Weighted average remaining maturity	9 days	10 days
Atlanta | BancTrust [Member] | Federal Home Loan Bank Advances
Debt Instrument [Line Items]
Number of outstanding short-term FHLB advances | Loan	0	0
Interest rate (in hundredths)	0.08%	0.08%
Debt instrument remaining maturity period	2 years 8 months 15 days	3 years 8 months 15 days
Number of outstanding long-term FHLB advances | Loan	1	1
Long-term FHLB advances	$ 58,000	$ 78,000
Atlanta | BancTrust [Member] | Fair Market Value Adjustment [Member] | Federal Home Loan Bank Advances
Debt Instrument [Line Items]
Fair value adjustment on FHLB advances	$ 0	$ 0
Dallas [Member] | Federal Home Loan Bank Advances
Debt Instrument [Line Items]
Number of outstanding short-term FHLB advances | Loan	5	4
Short-term FHLB advances	$ 400,000,000	$ 975,000,000
Long-term FHLB advances	0	0
Additional debt instrument borrowing capacity	4,003,000,000.000	3,034,000,000.000
Dallas [Member] | Short Term FhlbAdvances1 [Member] | Federal Home Loan Bank Advances
Debt Instrument [Line Items]
Short-term FHLB advances	$ 50,000,000
Interest rate (in hundredths)	5.38%
Dallas [Member] | Short Term FhlbAdvances2 [Member] | Federal Home Loan Bank Advances
Debt Instrument [Line Items]
Short-term FHLB advances	$ 125,000,000
Interest rate (in hundredths)	5.61%
Dallas [Member] | Fair Market Value Adjustment [Member] | Federal Home Loan Bank Advances
Debt Instrument [Line Items]
Interest expense, short-term borrowings		4,800,000
Dallas [Member] | BancTrust [Member] | Federal Home Loan Bank Advances
Debt Instrument [Line Items]
Interest expense, long-term borrowings	$ 0	$ 0	$ 0
Dallas [Member] | BancTrust [Member] | Fair Market Value Adjustment [Member]
Debt Instrument [Line Items]
Interest expense, short-term borrowings	$ 49,900,000		$ 2,000