Note Loans (Changes in the carrying amount and the accretable yield for the acquired loans in the Westernbank FDIC-assisted transaction) (Parenthetical) (Detail) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
ASC Subtopic 310-30 \| Remain Subject To The Loss Sharing Agreement With FDIC
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying amount	$ 505	$ 507	$ 542

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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