Acquisitions and Divestitures - Narrative (Details) $ in Thousands					3 Months Ended
	Nov. 08, 2019 USD ($) branch	Nov. 04, 2019 office state directors	Mar. 23, 2018 USD ($) branch	Nov. 30, 2017 USD ($) branch shares	Jun. 30, 2018 USD ($) shares	Sep. 30, 2019 USD ($)	Apr. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Business Acquisition [Line Items]
Assets						$ 43,717,684		$ 40,832,258
Loans						31,067,684		27,355,108
Deposits						31,944,660		32,682,992
Goodwill						1,432,787		$ 1,432,787	$ 1,409,822	$ 1,386,853
Portion of Sub-prime Auto Loan Portfolios
Business Acquisition [Line Items]
Loans disposed of									$ 120,000
Portion of Sub-prime Auto Loan Portfolios | Discontinued Operations, Disposed of by Sale
Business Acquisition [Line Items]
Loans disposed of					$ 120,000
Subprime Consumer Loans | Discontinued Operations, Held-for-sale
Business Acquisition [Line Items]
Loans disposed of							$ 25,000
Apex Bank
Business Acquisition [Line Items]
Number of branches divested | branch			2
Deposits disposed of			$ 30,000
Loans disposed of			$ 2,000
Capital Bank Financial Corp
Business Acquisition [Line Items]
Business acquisition, equity interest issued or issuable, number of shares (in shares) | shares				92,042,232
Payments to acquire businesses				$ 423,600	$ 46,000
Business combination, consideration transferred				$ 2,200,000
canceled common shares | shares					2,373,220
Number of bank branches | branch				178
Assets acquired				$ 9,900,000
Loans				7,300,000
Securities available-for-sale				1,200,000
Deposits				8,100,000
Goodwill				$ 1,200,000
Subsequent Event | IBERIABANK DIRECTORS
Business Acquisition [Line Items]
Number of board of directors | directors		8
Subsequent Event | IBERIABANK (IBKC)
Business Acquisition [Line Items]
Conversion price of shares		4.584
Conversion percentage of shares		44.00%
Number of board of directors | directors		17
Subsequent Event | IBERIABANK (IBKC) | FHN DIRECTORS
Business Acquisition [Line Items]
Number of board of directors | directors		9
Subsequent Event | SunTrust Banks, Inc. Branches
Business Acquisition [Line Items]
Number of bank branches | branch	30
Loans	$ 410,000
Deposits	$ 2,400,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deposits Premium Percent	3.40%
IBERIABANK (IBKC)
Business Acquisition [Line Items]
Assets						31,700,000
Loans						23,700,000
Deposits						$ 25,000,000
IBERIABANK (IBKC) | Subsequent Event
Business Acquisition [Line Items]
Number of offices | office		319
Number of states | state		12
NORTH CAROLINA | Subsequent Event | SunTrust Banks, Inc. Branches
Business Acquisition [Line Items]
Number of bank branches | branch	20
VIRGINIA | Subsequent Event | SunTrust Banks, Inc. Branches
Business Acquisition [Line Items]
Number of bank branches | branch	8
GEORGIA | Subsequent Event | SunTrust Banks, Inc. Branches
Business Acquisition [Line Items]
Number of bank branches | branch	2