Asset Quality - Changes in Liability for Credit Losses on Lending Related Commitments (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	$ 56	$ 35	$ 37
Provision (credit) for losses on lending-related commitments	(1)	21	(2)
Balance at end of period	$ 55	$ 56	$ 35

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

No definition available.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration