Loans - Non-Covered and Covered PCI Loans and Non-PCI Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable
Loans	$ 25,423,118	$ 25,035,469
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Loans	4,504,927	4,331,032
Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	14,119,624	13,895,407
Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	12,665,425	12,407,275
Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable
Loans	1,454,199	1,488,132
Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Loans	4,071,237	4,111,400
Consumer
Accounts, Notes, Loans and Financing Receivable
Loans	2,727,330	2,697,630
Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable
Loans	513,066	517,089
Consumer | Automobile
Accounts, Notes, Loans and Financing Receivable
Loans	1,347,759	1,319,571
Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable
Loans	866,505	860,970
Non-PCI Loans
Accounts, Notes, Loans and Financing Receivable
Loans	21,418,778	20,845,383
Non-PCI Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Loans	3,786,742	3,590,375
Non-PCI Loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	11,389,129	11,034,657
Non-PCI Loans | Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	10,189,388	9,912,309
Non-PCI Loans | Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable
Loans	1,199,741	1,122,348
Non-PCI Loans | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Loans	3,660,983	3,682,984
Non-PCI Loans | Consumer
Accounts, Notes, Loans and Financing Receivable
Loans	2,581,924	2,537,367
Non-PCI Loans | Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable
Loans	381,217	371,340
Non-PCI Loans | Consumer | Automobile
Accounts, Notes, Loans and Financing Receivable
Loans	1,347,405	1,319,206
Non-PCI Loans | Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable
Loans	853,302	846,821
PCI Loans
Accounts, Notes, Loans and Financing Receivable
Loans	4,004,340	4,190,086
PCI Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Loans	718,185	740,657
PCI Loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	2,730,495	2,860,750
PCI Loans | Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	2,476,037	2,494,966
PCI Loans | Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable
Loans	254,458	365,784
PCI Loans | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Loans	410,254	428,416
PCI Loans | Consumer
Accounts, Notes, Loans and Financing Receivable
Loans	145,406	160,263
PCI Loans | Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable
Loans	131,849	145,749
PCI Loans | Consumer | Automobile
Accounts, Notes, Loans and Financing Receivable
Loans	354	365
PCI Loans | Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable
Loans	$ 13,203	$ 14,149