Loans and Allowance for Loan Losses - Allowance for loan losses by portfolio (Details) - USD ($) $ in Thousands		Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Ending balance of allowance attributable to loans:
Individually evaluated for impairment		$ 137,351	$ 138,208
Collectively evaluated for impairment		696,755	700,085
Purchased loans, covered		0	0
Purchased loans, covered and not covered		0	0
Total allowance for loan losses, covered		0	0	$ 1,147	$ 1,440
Total allowance for loan losses, total loans		834,106	838,293	822,440	762,673
Ending balance of loans:
Individually evaluated for impairment		794,087	953,106
Collectively evaluated for impairment		58,529,124	58,702,930
Purchased loans, covered		341,939	359,334
Purchased loans, covered and not covered		382,556	405,227
Total loans, covered		341,939	359,334
Total loans		59,705,767	60,061,263
Commercial, Financial and Agricultural
Ending balance of allowance attributable to loans:
Individually evaluated for impairment		96,429	99,932
Collectively evaluated for impairment		362,785	358,648
Purchased loans		0	0
Total allowance for loan losses		459,214	458,580	467,638	402,113
Ending balance of loans:
Individually evaluated for impairment		553,976	719,468
Collectively evaluated for impairment		24,082,230	24,377,200
Purchased loans		24,462	25,334
Total loans		24,660,668	25,122,002
Commercial Real Estate
Ending balance of allowance attributable to loans:
Individually evaluated for impairment	[1]	7,225	4,037
Collectively evaluated for impairment	[1]	107,382	112,900
Purchased loans	[1]	0	0
Total allowance for loan losses	[1]	114,607	116,937	115,931	122,068
Ending balance of loans:
Individually evaluated for impairment	[1]	61,172	44,258
Collectively evaluated for impairment	[1]	13,553,116	13,275,968
Purchased loans	[1]	11,938	15,750
Total loans	[1]	13,626,226	13,335,976
Residential Real Estate
Ending balance of allowance attributable to loans:
Individually evaluated for impairment	[2]	31,746	32,016
Collectively evaluated for impairment	[2]	84,199	87,468
Purchased loans	[2]	0	0
Total allowance for loan losses	[2]	115,945	119,484	125,173	132,104
Ending balance of loans:
Individually evaluated for impairment	[2]	176,269	186,338
Collectively evaluated for impairment	[2]	15,922,100	16,062,554
Purchased loans	[2]	264	589
Total loans	[2]	16,098,633	16,249,481
Consumer
Ending balance of allowance attributable to loans:
Individually evaluated for impairment	[3]	1,951	2,223
Collectively evaluated for impairment	[3]	142,389	141,069
Purchased loans	[3]	0	0
Total allowance for loan losses	[3]	144,340	143,292	$ 112,551	$ 104,948
Ending balance of loans:
Individually evaluated for impairment	[3]	2,670	3,042
Collectively evaluated for impairment	[3]	4,971,678	4,987,208
Purchased loans	[3]	3,953	4,220
Total loans	[3]	$ 4,978,301	$ 4,994,470

[1] Includes commercial real estate – mortgage and real estate – construction loans.

[2] Includes residential real estate – mortgage, equity lines of credit and equity loans.

[3] Includes credit card, consumer direct and consumer indirect loans.