Business Segment Information - Amounts of Consolidated Revenue, Expense, Tax and Assets (Details) - USD ($) $ in Millions		12 Months Ended
	Jul. 01, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Net interest income (expense)		$ 1,994	$ 1,662	$ 1,210
Provision for credit losses		(310)	503	45
Noninterest income		1,076	1,492	654
Noninterest expense		2,096	1,718	1,233
Income before income taxes		1,284	933	586
Income tax expense (benefit)		274	76	134
Net income (loss)		1,010	857	452
Average assets		87,609	64,346	41,744
Depreciation and amortization		28	46	65
Expenditures for long-lived assets		37	379	49
Purchase accounting gain		(1)	533	0
Long-lived asset impairment				13
Expenses associated with rebranding initiatives				25
Charitable foundation contributions			41	11
Parent Company
Segment Reporting Information [Line Items]
Provision for credit losses		0	0	(1)
Income before income taxes		624	87	264
Income tax expense (benefit)		(35)	(18)	(19)
Depreciation and amortization		0	0	(1)
Visa Class B Shares
Segment Reporting Information [Line Items]
Derivative valuation adjustment		19
IBERIABANK (IBKC)
Segment Reporting Information [Line Items]
Purchase accounting gain	$ 531		533
Regional Banking
Segment Reporting Information [Line Items]
Net interest income (expense)		1,764	1,264	833
Provision for credit losses		(229)	392	24
Noninterest income		438	345	293
Noninterest expense		1,151	944	678
Income before income taxes		1,280	273	424
Income tax expense (benefit)		298	56	97
Net income (loss)		982	217	327
Average assets		45,445	32,782	18,236
Depreciation and amortization		(71)	(42)	22
Expenditures for long-lived assets		27	283	29
Purchase accounting gain		0	0
Specialty Banking
Segment Reporting Information [Line Items]
Net interest income (expense)		619	572	389
Provision for credit losses		(64)	116	37
Noninterest income		597	576	315
Noninterest expense		571	494	347
Income before income taxes		709	538	320
Income tax expense (benefit)		171	131	79
Net income (loss)		538	407	241
Average assets		20,803	19,822	15,517
Depreciation and amortization		(2)	4	14
Expenditures for long-lived assets		3	6	4
Purchase accounting gain		0	0
Corporate
Segment Reporting Information [Line Items]
Net interest income (expense)		(389)	(174)	(12)
Provision for credit losses		(17)	(5)	(16)
Noninterest income		41	571	46
Noninterest expense		374	280	208
Income before income taxes		(705)	122	(158)
Income tax expense (benefit)		(195)	(111)	(42)
Net income (loss)		(510)	233	(116)
Average assets		21,361	11,742	7,991
Depreciation and amortization		101	84	29
Expenditures for long-lived assets		7	90	16
Purchase accounting gain		(1)	533
Long-lived asset impairment		37	$ 13
Corporate | Visa Class B Shares
Segment Reporting Information [Line Items]
Derivative valuation adjustment		$ 19		$ 4