Loans and Allowance for Loan Losses - Allowance for loan losses by portfolio (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		$ 920,993	$ 885,242
Provision for loan losses		356,946	182,292
Loans charged-off		(142,159)	(127,413)
Loan recoveries		30,361	25,901
Net charge-offs		(111,798)	(101,512)
Balance at end of period		1,351,072	966,022
Ending balance of allowance attributable to loans:
Individually evaluated for impairment				$ 126,832
Collectively evaluated for impairment				794,161
Total allowance for loan losses		1,351,072		920,993
Ending balance of loans:
Individually evaluated for impairment				486,044
Collectively evaluated for impairment				63,460,813
Total		67,539,414		63,946,857
Commercial, Financial and Agricultural
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		408,197	393,315
Provision for loan losses		140,413	59,180
Loans charged-off		(24,207)	(9,503)
Loan recoveries		5,193	4,760
Net charge-offs		(19,014)	(4,743)
Balance at end of period		547,985	447,752
Ending balance of allowance attributable to loans:
Individually evaluated for impairment				88,164
Collectively evaluated for impairment				320,033
Total allowance for loan losses				408,197
Ending balance of loans:
Individually evaluated for impairment				238,653
Collectively evaluated for impairment				24,193,585
Total		27,832,113		24,432,238
Commercial Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	[1]	118,633	112,437
Provision for loan losses	[1]	24,548	4,662
Loans charged-off	[1]	(87)	(25)
Loan recoveries	[1]	173	1,462
Net charge-offs	[1]	86	1,437
Balance at end of period	[1]	108,233	118,536
Ending balance of allowance attributable to loans:
Individually evaluated for impairment	[1]			13,255
Collectively evaluated for impairment	[1]			105,378
Total allowance for loan losses	[1]			118,633
Ending balance of loans:
Individually evaluated for impairment	[1]			78,301
Collectively evaluated for impairment	[1]			15,811,859
Total	[1]			15,890,160
Residential Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	[2]	99,089	101,929
Provision for loan losses	[2]	7,032	2,183
Loans charged-off	[2]	(1,999)	(5,012)
Loan recoveries	[2]	1,423	3,589
Net charge-offs	[2]	(576)	(1,423)
Balance at end of period	[2]	152,935	102,689
Ending balance of allowance attributable to loans:
Individually evaluated for impairment	[2]			22,775
Collectively evaluated for impairment	[2]			76,314
Total allowance for loan losses	[2]			99,089
Ending balance of loans:
Individually evaluated for impairment	[2]			155,728
Collectively evaluated for impairment	[2]			16,215,874
Total	[2]			16,371,602
Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	[3]	295,074	277,561
Provision for loan losses	[3]	184,953	116,267
Loans charged-off	[3]	(115,866)	(112,873)
Loan recoveries	[3]	23,572	16,090
Net charge-offs	[3]	(92,294)	(96,783)
Balance at end of period	[3]	541,919	$ 297,045
Ending balance of allowance attributable to loans:
Individually evaluated for impairment	[3]			2,638
Collectively evaluated for impairment	[3]			292,436
Total allowance for loan losses	[3]			295,074
Ending balance of loans:
Individually evaluated for impairment	[3]			13,362
Collectively evaluated for impairment	[3]			7,239,495
Total	[3]			$ 7,252,857
Impact of ASC 326 Adoption
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		184,931
Impact of ASC 326 Adoption | Commercial, Financial and Agricultural
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		18,389
Impact of ASC 326 Adoption | Commercial Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	[1]	(35,034)
Impact of ASC 326 Adoption | Residential Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	[2]	47,390
Impact of ASC 326 Adoption | Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	[3]	154,186
As Reported Under ASC 326
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		1,105,924
As Reported Under ASC 326 | Commercial, Financial and Agricultural
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		426,586
As Reported Under ASC 326 | Commercial Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	[1]	83,599
As Reported Under ASC 326 | Residential Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	[2]	146,479
As Reported Under ASC 326 | Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	[3]	$ 449,260

[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.