Loans - Non-Covered and Covered PCI Loans and Non-PCI Loans (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable
Loans	$ 25,802,162	$ 25,035,469
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Loans	4,615,765	4,331,032
Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	14,326,985	13,895,407
Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	12,798,017	12,407,275
Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable
Loans	1,528,968	1,488,132
Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Loans	4,072,450	4,111,400
Consumer
Accounts, Notes, Loans and Financing Receivable
Loans	2,786,962	2,697,630
Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable
Loans	501,646	517,089
Consumer | Automobile
Accounts, Notes, Loans and Financing Receivable
Loans	1,362,466	1,319,571
Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable
Loans	922,850	860,970
Non-PCI Loans
Accounts, Notes, Loans and Financing Receivable
Loans	22,030,205	20,845,383
Non-PCI Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Loans	3,918,894	3,590,375
Non-PCI Loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	11,758,544	11,034,657
Non-PCI Loans | Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	10,470,127	9,912,309
Non-PCI Loans | Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable
Loans	1,288,417	1,122,348
Non-PCI Loans | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Loans	3,694,463	3,682,984
Non-PCI Loans | Consumer
Accounts, Notes, Loans and Financing Receivable
Loans	2,658,304	2,537,367
Non-PCI Loans | Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable
Loans	385,987	371,340
Non-PCI Loans | Consumer | Automobile
Accounts, Notes, Loans and Financing Receivable
Loans	1,362,143	1,319,206
Non-PCI Loans | Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable
Loans	910,174	846,821
PCI Loans
Accounts, Notes, Loans and Financing Receivable
Loans	3,771,957	4,190,086
PCI Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Loans	696,871	740,657
PCI Loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	2,568,441	2,860,750
PCI Loans | Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	2,327,890	2,494,966
PCI Loans | Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable
Loans	240,551	365,784
PCI Loans | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Loans	377,987	428,416
PCI Loans | Consumer
Accounts, Notes, Loans and Financing Receivable
Loans	128,658	160,263
PCI Loans | Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable
Loans	115,659	145,749
PCI Loans | Consumer | Automobile
Accounts, Notes, Loans and Financing Receivable
Loans	323	365
PCI Loans | Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable
Loans	$ 12,676	$ 14,149