Other Short-Term Borrowings (Other Short-Term Borrowings - Additioanl Information) (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Debt Current [Abstract]
Securities sold under repurchase agreements	$ 287	$ 546

Amount, after the effects of master netting arrangements, of funds outstanding borrowed in the form of a security repurchase agreement between the entity and another party for the sale and repurchase of identical or substantially the same securities at a date certain for a specified price. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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Name:	us-gaap_SecuritiesSoldUnderAgreementsToRepurchase
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant