Regulatory Capital (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Capital conservation buffer	2.50%
Capital conservation buffer period	3 years
Significant subsidiary, assets or net income as percentage of consolidated total, threshold	10.00%
Common equity tier 1 capital
Common equity tier 1 capital, Actual	$ 2,763,168	$ 2,654,287
Common equity tier 1 capital, For Capital Adequacy Purposes	1,250,488	1,199,794
Tier 1 capital
Tier I capital, Actual	2,872,001	2,685,880
Tier I capital, For Capital Adequacy Purposes	1,660,074	1,599,725
Total risk-based capital
Total risk-based capital, Actual	3,383,081	3,201,268
Total risk-based capital, For Capital Adequacy Purposes	$ 2,213,432	$ 2,132,966
Common equity tier 1 capital ratio
Common equity tier I capital ratio, Actual	9.99%	9.96%
Common equity tier I capital ratio, For Capital Adequacy Purposes	4.50%	4.50%
Tier 1 capital ratio
Tier 1 capital ratio, Actual	10.38%	10.07%
Tier 1 capital ratio, For Capital Adequacy Purposes	6.00%	6.00%
Total risk-based capital ratio
Total risk-based capital ratio, Actual	12.23%	12.01%
Total risk-based capital ratio, For Capital Adequacy Purposes	8.00%	8.00%
Leverage ratio
Leverage ratio, Actual	9.19%	8.99%
Leverage ratio, For Capital Adequacy Purposes	4.00%	4.00%
Minimum
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Capital conservation buffer	0.625%
Well-capitalized status,Tier 1 capital ratio	8.00%
Common equity tier 1 capital ratio
Common equity tier I capital ratio, To Be Well Capitalized Under Prompt Corrective Action Provisions	6.50%
Total risk-based capital ratio
Total risk-based capital ratio, To Be Well Capitalized Under Prompt Corrective Action Provisions	10.00%
Leverage ratio
Leverage ratio, To Be Well Capitalized Under Prompt Corrective Action Provisions	5.00%
Synovus Bank Reporting Unit
Common equity tier 1 capital
Common equity tier 1 capital, Actual	$ 3,155,163	$ 3,187,583
Common equity tier 1 capital, For Capital Adequacy Purposes	1,247,462	1,197,976
Common equity tier 1 capital, To Be Well Capitalized Under Prompt Corrective Action Provisions	1,795,004	1,730,410
Tier 1 capital
Tier I capital, Actual	3,155,163	3,187,583
Tier I capital, For Capital Adequacy Purposes	1,656,927	1,597,302
Tier I capital, To Be Well Capitalized Under Prompt Corrective Action Provisions	2,209,236	2,129,736
Total risk-based capital
Total risk-based capital, Actual	3,406,243	3,441,563
Total risk-based capital, For Capital Adequacy Purposes	2,209,236	2,129,736
Total risk-based capital, To Be Well Capitalized Under Prompt Corrective Action Provisions	$ 2,761,545	$ 2,662,169
Common equity tier 1 capital ratio
Common equity tier I capital ratio, Actual	11.43%	11.97%
Common equity tier I capital ratio, For Capital Adequacy Purposes	4.50%	4.50%
Common equity tier I capital ratio, To Be Well Capitalized Under Prompt Corrective Action Provisions	6.50%	6.50%
Tier 1 capital ratio
Tier 1 capital ratio, Actual	11.43%	11.97%
Tier 1 capital ratio, For Capital Adequacy Purposes	6.00%	6.00%
Tier 1 capital ratio, To Be Well Capitalized Under Prompt Corrective Action Provisions	8.00%	8.00%
Total risk-based capital ratio
Total risk-based capital ratio, Actual	12.33%	12.93%
Total risk-based capital ratio, For Capital Adequacy Purposes	8.00%	8.00%
Total risk-based capital ratio, To Be Well Capitalized Under Prompt Corrective Action Provisions	10.00%	10.00%
Leverage ratio
Leverage ratio, Actual	10.12%	10.68%
Leverage ratio, For Capital Adequacy Purposes	4.00%	4.00%
Leverage ratio, To Be Well Capitalized Under Prompt Corrective Action Provisions	5.00%	5.00%