Loans - Non-Covered and Covered PCI Loans and Non-PCI Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable
Loans	$ 26,567,159	$ 25,035,469
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Loans	4,695,608	4,331,032
Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	14,903,044	13,895,407
Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	13,365,454	12,407,275
Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable
Loans	1,537,590	1,488,132
Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Loans	4,133,331	4,111,400
Consumer
Accounts, Notes, Loans and Financing Receivable
Loans	2,835,176	2,697,630
Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable
Loans	489,808	517,089
Consumer | Automobile
Accounts, Notes, Loans and Financing Receivable
Loans	1,436,608	1,319,571
Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable
Loans	908,760	860,970
Non-PCI Loans
Accounts, Notes, Loans and Financing Receivable
Loans	23,029,991	20,845,383
Non-PCI Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Loans	4,038,064	3,590,375
Non-PCI Loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	12,506,395	11,034,657
Non-PCI Loans | Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	11,121,325	9,912,309
Non-PCI Loans | Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable
Loans	1,385,070	1,122,348
Non-PCI Loans | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Loans	3,770,500	3,682,984
Non-PCI Loans | Consumer
Accounts, Notes, Loans and Financing Receivable
Loans	2,715,032	2,537,367
Non-PCI Loans | Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable
Loans	382,079	371,340
Non-PCI Loans | Consumer | Automobile
Accounts, Notes, Loans and Financing Receivable
Loans	1,436,313	1,319,206
Non-PCI Loans | Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable
Loans	896,640	846,821
PCI Loans
Accounts, Notes, Loans and Financing Receivable
Loans	3,537,168	4,190,086
PCI Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Loans	657,544	740,657
PCI Loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	2,396,649	2,860,750
PCI Loans | Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	2,244,129	2,494,966
PCI Loans | Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable
Loans	152,520	365,784
PCI Loans | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Loans	362,831	428,416
PCI Loans | Consumer
Accounts, Notes, Loans and Financing Receivable
Loans	120,144	160,263
PCI Loans | Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable
Loans	107,729	145,749
PCI Loans | Consumer | Automobile
Accounts, Notes, Loans and Financing Receivable
Loans	295	365
PCI Loans | Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable
Loans	$ 12,120	$ 14,149