Goodwill and Other Intangible Assets - Summary of Goodwill Assigned to Reportable Segments for Purposes of Testing for Impairment (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Goodwill [Line Items]
Goodwill	$ 4,593,112	$ 4,593,112
Business Banking [Member]
Goodwill [Line Items]
Goodwill	864,366	864,366
Commercial Banking [Member]
Goodwill [Line Items]
Goodwill	1,401,873	1,401,873
Commercial Real Estate [Member]
Goodwill [Line Items]
Goodwill	654,389	654,389
Retail Banking [Member]
Goodwill [Line Items]
Goodwill	1,309,191	1,309,191
All Other [Member]
Goodwill [Line Items]
Goodwill	$ 363,293	$ 363,293