Loans and Allowance for Loan Losses - Past due loans (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual, Covered	$ 410	$ 730
Accruing TDRs, Covered	0	0
Total Past Due and Impaired, Covered	34,010	36,630
Not Past Due or Impaired, Covered	307,929	322,704
Total loans, covered	341,939	359,334
Nonaccrual, Total Loans	825,988	864,450
Accruing TDRs, Total Loans	129,743	111,322
Total Past Due and Impaired, Total Loans	1,297,076	1,327,735
Not Past Due or Impaired, Total Loans	58,408,691	58,733,528
Total loans	59,705,767	60,061,263
30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due, Covered	6,448	7,311
Financing Receivable, Past Due, Total Loans	205,900	211,651
60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due, Covered	3,479	1,351
Financing Receivable, Past Due, Total Loans	69,828	78,770
90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due, Covered	23,673	27,238
Financing Receivable, Past Due, Total Loans	65,617	61,542
Commercial, Financial and Agricultural
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual	540,407	596,454
Accruing TDRs	31,644	8,726
Total Past Due and Impaired	610,732	638,440
Not Past Due or Impaired	24,049,936	24,483,562
Total	24,660,668	25,122,002
Commercial, Financial and Agricultural | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	22,472	23,788
Commercial, Financial and Agricultural | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	11,804	6,581
Commercial, Financial and Agricultural | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	4,405	2,891
Commercial Real Estate | Real estate – construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual	1,028	1,239
Accruing TDRs	114	2,393
Total Past Due and Impaired	5,294	6,607
Not Past Due or Impaired	2,222,111	2,118,709
Total	2,227,405	2,125,316
Commercial Real Estate | Real estate – construction | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	487	918
Commercial Real Estate | Real estate – construction | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	25	50
Commercial Real Estate | Real estate – construction | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	3,640	2,007
Commercial Real Estate | Commercial real estate – mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual	89,908	71,921
Accruing TDRs	4,821	4,860
Total Past Due and Impaired	114,429	84,046
Not Past Due or Impaired	11,284,392	11,126,614
Total	11,398,821	11,210,660
Commercial Real Estate | Commercial real estate – mortgage | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	13,872	3,791
Commercial Real Estate | Commercial real estate – mortgage | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	1,226	3,474
Commercial Real Estate | Commercial real estate – mortgage | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	4,602	0
Residential Real Estate | Residential real estate – mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual	140,342	140,303
Accruing TDRs	58,867	59,893
Total Past Due and Impaired	285,433	289,361
Not Past Due or Impaired	12,832,343	12,970,633
Total	13,117,776	13,259,994
Residential Real Estate | Residential real estate – mortgage | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	61,234	57,359
Residential Real Estate | Residential real estate – mortgage | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	22,337	28,450
Residential Real Estate | Residential real estate – mortgage | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	2,653	3,356
Residential Real Estate | Equity lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual	32,675	33,453
Accruing TDRs	0	0
Total Past Due and Impaired	46,916	48,908
Not Past Due or Impaired	2,513,579	2,494,870
Total	2,560,495	2,543,778
Residential Real Estate | Equity lines of credit | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	9,144	7,922
Residential Real Estate | Equity lines of credit | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	3,619	4,583
Residential Real Estate | Equity lines of credit | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	1,478	2,950
Residential Real Estate | Equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual	12,626	13,635
Accruing TDRs	33,635	34,746
Total Past Due and Impaired	53,334	56,306
Not Past Due or Impaired	367,028	389,403
Total	420,362	445,709
Residential Real Estate | Equity loans | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	5,105	5,615
Residential Real Estate | Equity loans | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	1,592	1,843
Residential Real Estate | Equity loans | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	376	467
Consumer | Credit card
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual	0	0
Accruing TDRs	0	0
Total Past Due and Impaired	23,434	22,407
Not Past Due or Impaired	546,877	582,474
Total	570,311	604,881
Consumer | Credit card | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	6,262	6,411
Consumer | Credit card | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	4,719	5,042
Consumer | Credit card | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	12,453	10,954
Consumer | Consumer direct
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual	637	789
Accruing TDRs	662	704
Total Past Due and Impaired	23,064	23,876
Not Past Due or Impaired	1,306,178	1,230,765
Total	1,329,242	1,254,641
Consumer | Consumer direct | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	12,025	13,338
Consumer | Consumer direct | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	4,866	4,563
Consumer | Consumer direct | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	4,874	4,482
Consumer | Consumer indirect
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual	7,955	5,926
Accruing TDRs	0	0
Total Past Due and Impaired	100,430	121,154
Not Past Due or Impaired	2,978,318	3,013,794
Total	3,078,748	3,134,948
Consumer | Consumer indirect | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	68,851	85,198
Consumer | Consumer indirect | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	16,161	22,833
Consumer | Consumer indirect | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	$ 7,463	$ 7,197