Note Loans (Changes in the carrying amount and the accretable yield for the acquired loans in the Westernbank FDIC-assisted transaction) (Parenthetical) (Detail) - ASC Subtopic 310-30 - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2016	Sep. 30, 2017	Dec. 31, 2016
Westernbank Puerto Rico | Bulk Sale
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Sold	$ 99	$ 99
Remain Subject To The Loss Sharing Agreement With FDIC
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying amount	$ 578	$ 578	$ 515	$ 563