Acquisitions and Divestitures (Narrative) (Details) $ in Thousands				3 Months Ended	6 Months Ended
	Mar. 23, 2018 USD ($) branch	Nov. 30, 2017 USD ($) branch shares	Apr. 03, 2017 USD ($)	Jun. 30, 2018 USD ($) shares	Jun. 30, 2018 USD ($) branch	Dec. 31, 2017 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)
Business Acquisition [Line Items]
Goodwill				$ 1,409,276	$ 1,409,276	$ 1,386,853	$ 236,335	$ 191,371
Number of branches divested | branch					2
Deposits disposed of						$ 22,600
Portion of Sub-prime Auto Loan Portfolios
Business Acquisition [Line Items]
Loans disposed of				120,000	$ 120,000
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	469,609
Business combination, consideration transferred		$ 2,200,000			2,216,333
Business acquisition, number of shares canceled (in shares) | shares				2,373,220
Number of bank branches | branch		178
Assets acquired		$ 9,900,000		$ 9,858,145	9,858,145
Loans		7,300,000		7,276,544	7,276,544
Securities available-for-sale		1,200,000		1,193,393	1,193,393
Deposits		$ 8,100,000		8,140,102	8,140,102
Goodwill				1,169,324	1,169,324
Loans held-for-sale				124,918	124,918
Trading securities				0	0
Securities sold under agreements to repurchase				$ 26,664	$ 26,664
Coastal Securities, Inc
Business Acquisition [Line Items]
Payments to acquire businesses			$ 131,000
Assets acquired			418,000
Goodwill			45,000
Loans held-for-sale			236,000
Trading securities			139,000
Securities sold under agreements to repurchase			202,000
Fixed income payables			$ 96,000