Acquisitions and Divestitures - Purchase Price Allocation (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended		12 Months Ended
	Jul. 01, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Consideration paid:
Purchase accounting gain		$ 0	$ (532)	$ 1	$ (532)
IBERIABANK (IBKC)
Assets:
Cash and due from banks	$ 395
Interest-bearing deposits with banks	1,683
Securities available for sale at fair value	3,544
Loans held for sale	320
Loans and leases	25,921
Allowance for loan and lease losses	(284)
Other intangible assets	240
Premises and equipment	311
OREO	9
Other assets	1,153
Total assets acquired	33,292
Liabilities:
Deposits	28,232
Short-term borrowings	209
Term borrowings	1,200
Other liabilities	618
Total liabilities assumed	30,259
Net assets acquired	3,033
Consideration paid:
Total consideration paid	2,502
Purchase accounting gain	(531)					$ (531)
IBERIABANK (IBKC) | Equity awards
Consideration paid:
Consideration for outstanding common stock	28
IBERIABANK (IBKC) | Commercial | Sales-Type And Direct Financing Leases
Assets:
Loans and leases	1,300
IBERIABANK (IBKC) | Common Stock
Consideration paid:
Consideration for outstanding common stock	2,243
IBERIABANK (IBKC) | Preferred Stock
Consideration paid:
Consideration for outstanding common stock	$ 231