Loans and Allowance for Loan Losses - Allowance for loan losses by portfolio (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		$ 1,351,072	$ 966,022	$ 920,993	$ 885,242
Provision for loan losses		526,334	155,018	883,280	337,310
Loans charged-off		(139,011)	(164,871)	(281,170)	(292,284)
Loan recoveries		15,957	21,491	46,318	47,392
Net (charge-offs) recoveries		(123,054)	(143,380)	(234,852)	(244,892)
Balance at end of period		1,754,352	977,660	1,754,352	977,660
Ending balance of allowance attributable to loans:
Individually evaluated for impairment						$ 126,832
Collectively evaluated for impairment						794,161
Total allowance for loan losses		1,754,352		1,754,352		920,993
Ending balance of loans:
Individually evaluated for impairment						486,044
Collectively evaluated for impairment						63,460,813
Total		68,241,500		68,241,500		63,946,857
Commercial, Financial and Agricultural
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period		547,985	447,752	408,197	393,315
Provision for loan losses		238,565	54,218	378,978	113,398
Loans charged-off		(30,970)	(49,325)	(55,177)	(58,828)
Loan recoveries		1,932	3,409	7,125	8,169
Net (charge-offs) recoveries		(29,038)	(45,916)	(48,052)	(50,659)
Balance at end of period		757,512	456,054	757,512	456,054
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		28,782,124		28,782,124		24,432,238
Commercial Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	[1]	108,233	118,536	118,633	112,437
Provision for loan losses	[1]	128,276	(1,166)	152,824	3,496
Loans charged-off	[1]	(9,053)	(112)	(9,140)	(137)
Loan recoveries	[1]	419	528	592	1,990
Net (charge-offs) recoveries	[1]	(8,634)	416	(8,548)	1,853
Balance at end of period	[1]	227,875	117,786	227,875	117,786
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]	152,935	102,689	99,089	101,929
Provision for loan losses	[2]	30,136	(250)	37,168	1,933
Loans charged-off	[2]	(1,095)	(4,679)	(3,094)	(9,691)
Loan recoveries	[2]	1,509	2,591	2,932	6,180
Net (charge-offs) recoveries	[2]	414	(2,088)	(162)	(3,511)
Balance at end of period	[2]	183,485	100,351	183,485	100,351
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]	541,919	297,045	295,074	277,561
Provision for loan losses	[3]	129,357	102,216	314,310	218,483
Loans charged-off	[3]	(97,893)	(110,755)	(213,759)	(223,628)
Loan recoveries	[3]	12,097	14,963	35,669	31,053
Net (charge-offs) recoveries	[3]	(85,796)	(95,792)	(178,090)	(192,575)
Balance at end of period	[3]	$ 585,480	$ 303,469	585,480	$ 303,469
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.