Business Segment Information - Amounts of Consolidated Revenue, Expense, Tax and Assets (Details) - USD ($) $ in Millions		12 Months Ended
	Jul. 01, 2020	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
Net interest income (expense)		$ 2,392	$ 1,994	$ 1,662
Provision for credit losses		95	(310)	503
Noninterest income		815	1,076	1,492
Noninterest expense		1,953	2,096	1,718
Income before income taxes		1,159	1,284	933
Income tax expense (benefit)		247	274	76
Net income (loss)		912	1,010	857
Average assets		84,217	87,609	64,346
Depreciation and amortization		64	28	46
Expenditures for long-lived assets		24	37	379
Gain on sale of title services business		22	0	0
Purchase accounting gain		0	(1)	533
Charitable foundation contributions				41
Visa Class B Shares
Segment Reporting Information [Line Items]
Derivative valuation adjustment		22	19
IBERIABANK (IBKC)
Segment Reporting Information [Line Items]
Purchase accounting gain	$ 531			533
Regional Banking
Segment Reporting Information [Line Items]
Net interest income (expense)		1,954	1,764	1,287
Provision for credit losses		94	(229)	392
Noninterest income		444	438	345
Noninterest expense		1,234	1,139	903
Income before income taxes		1,070	1,292	337
Income tax expense (benefit)		251	303	73
Net income (loss)		819	989	264
Average assets		42,295	41,527	31,890
Depreciation and amortization		11	(67)	(39)
Expenditures for long-lived assets		18	27	283
Purchase accounting gain			0	0
Specialty Banking
Segment Reporting Information [Line Items]
Net interest income (expense)		557	620	576
Provision for credit losses		14	(64)	116
Noninterest income		311	597	576
Noninterest expense		440	571	498
Income before income taxes		414	710	538
Income tax expense (benefit)		101	171	131
Net income (loss)		313	539	407
Average assets		19,967	20,789	19,809
Depreciation and amortization		(7)	(3)	3
Expenditures for long-lived assets		12	3	6
Purchase accounting gain			0	0
Corporate
Segment Reporting Information [Line Items]
Net interest income (expense)		(119)	(390)	(201)
Provision for credit losses		(13)	(17)	(5)
Noninterest income		60	41	571
Noninterest expense		279	386	317
Income before income taxes		(325)	(718)	58
Income tax expense (benefit)		(105)	(200)	(128)
Net income (loss)		(220)	(518)	186
Average assets		21,955	25,293	12,647
Depreciation and amortization		60	98	82
Expenditures for long-lived assets		(6)	7	90
Gain on sale of title services business		22
Purchase accounting gain			(1)	533
Long-lived asset impairment			37	13
Corporate | Visa Class B Shares
Segment Reporting Information [Line Items]
Derivative valuation adjustment		22	19
Corporate | IBERIABANK Corporation and TD Merger
Segment Reporting Information [Line Items]
Merger and integration expense		$ 136	$ 187	$ 155