Acquisitions and Divestitures - Narrative (Details) $ in Thousands						3 Months Ended	7 Months Ended	12 Months Ended
	Nov. 08, 2019 USD ($) branch	Nov. 04, 2019 office state directors	Mar. 23, 2018 USD ($) branch	Nov. 30, 2017 USD ($) branch shares	Apr. 03, 2017 USD ($)	Jun. 30, 2018 USD ($) shares	Jun. 30, 2018 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Apr. 30, 2019 USD ($)
Business Acquisition [Line Items]
Assets								$ 43,310,900	$ 40,832,258
Loans								30,860,804	27,355,108
Deposits								32,429,535	32,682,992
Goodwill								1,432,787	1,432,787	$ 1,386,853	$ 191,371
Goodwill expected to be tax deductible				$ 17,000
Noninterest expense								1,210,187	1,220,317	842,314
IBERIABANK Corporation
Business Acquisition [Line Items]
Conversion price of shares		4.584
Conversion percentage of shares		44.00%
Number of board of directors | directors		17
SunTrust Banks, Inc. Branches
Business Acquisition [Line Items]
Number of bank branches | branch	30
Deposits	$ 2,400,000
Deposits premium percent	3.40%
Loans	$ 410,000
Capital Bank Financial Corporation
Business Acquisition [Line Items]
Number of bank branches | branch				178
Deposits				$ 8,140,102
Loans				$ 7,276,544
Equity interest issued, number of shares (in shares) | shares				92,042,232
Payments to acquire business				$ 423,600		$ 46,000	$ 469,615
Total consideration paid				2,216,333
Number of shares canceled (in shares) | shares						2,373,220
Assets acquired				9,833,737
Securities available-for-sale				1,193,393
Goodwill				$ 1,192,839
Acquired finite-lived intangible assets, weighted average useful life				10 years
Coastal Securities, Inc
Business Acquisition [Line Items]
Payments to acquire business					$ 131,473
Assets acquired					418,418
Goodwill					$ 44,964
IBERIABANK DIRECTORS
Business Acquisition [Line Items]
Number of board of directors | directors		8
FHN DIRECTORS | IBERIABANK Corporation
Business Acquisition [Line Items]
Number of board of directors | directors		9
Apex Bank
Business Acquisition [Line Items]
Number of branches divested | branch			2
Savings classified as held for sale			$ 30,000
Loans disposed of			$ 2,000
Portion of Sub-prime Auto Loan Portfolios
Business Acquisition [Line Items]
Loans disposed of						$ 120,000	$ 120,000		$ 120,000
Discontinued Operations, Held-for-sale | Subprime Consumer Loans
Business Acquisition [Line Items]
Loans disposed of												$ 25,000
Amortization Of Premiums And Accretion Of Discounts | Capital Bank Financial Corporation
Business Acquisition [Line Items]
Noninterest expense										34,500	46,500
Eliminate Amortization Of Premiums And Accretion Of Discounts | Capital Bank Financial Corporation
Business Acquisition [Line Items]
Noninterest expense										24,400	25,900
Amortization Of Acquired Intangibles | Capital Bank Financial Corporation
Business Acquisition [Line Items]
Noninterest expense										$ 15,800	$ 18,000
IBERIABANK Corporation
Business Acquisition [Line Items]
Number of offices | office		319
Number of states | state		12
Assets								31,700,000
Loans								24,000,000
Deposits								$ 25,200,000
NORTH CAROLINA | SunTrust Banks, Inc. Branches
Business Acquisition [Line Items]
Number of bank branches | branch	20
VIRGINIA | SunTrust Banks, Inc. Branches
Business Acquisition [Line Items]
Number of bank branches | branch	8
GEORGIA | SunTrust Banks, Inc. Branches
Business Acquisition [Line Items]
Number of bank branches | branch	2