Share-based Compensation and Other Employment Benefit Plans (Grants Under All Synovus Equity Compensation Plan) (Details) - Shareholder approved equity compensation plans for shares of Synovus stock	12 Months Ended
	Dec. 31, 2020 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of securities to be issued upon vesting of restricted share units (in shares)	1,660,000
Number of securities to be issued upon exercise of outstanding options (in shares)	2,401,000
Weighted-average exercise price of outstanding options (in dollars per share) | $ / shares	$ 22.47
Number of shares remaining available for issuance excluding shares discussed (in shares)	1,522,000
FCB Financial Holdings, Inc.
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of securities to be issued upon exercise of outstanding options (in shares)	2,000,000.0
Weighted average exercise price of options granted (in dollars per share) | $ / shares	$ 23.67