Note Guarantees (Indemnification, Representations and Warranties related to loans sold) - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Securitization \| Guarantee on loans sold or serviced with representation and warranties
Guarantor Obligations [Line Items]
Repurchased Loans	$ 1	$ 0	$ 10	$ 0

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.

No definition available.

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration