Acquisitions and Divestitures - Narrative (Details) $ in Thousands			3 Months Ended
	Mar. 23, 2018 USD ($) branch	Nov. 30, 2017 USD ($) branch shares	Jun. 30, 2018 USD ($) shares	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Business Acquisition [Line Items]
Goodwill			$ 1,409,276	$ 1,432,787		$ 1,432,787	$ 1,386,853
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
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares Canceled | 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
Apex Bank
Business Acquisition [Line Items]
Number of branches divested | branch	2
Deposits disposed of	$ 30,000
Loans disposed of	$ 2,000
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