Borrowings (Short-Term) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Short-term Debt [Line Items]
Short-term borrowings	$ 641,487	$ 738,233
Additional secured debt available	11,310,000
Securities sold under customer repurchase agreements
Short-term Debt [Line Items]
Short-term borrowings	641,487	442,956
Notes payable to FHLB of Atlanta
Short-term Debt [Line Items]
Short-term borrowings	0	255,000
Other short-term debt
Short-term Debt [Line Items]
Short-term borrowings	0	$ 40,277
Unsecured Debt
Short-term Debt [Line Items]
Accessible overnight borrowings	$ 598,000