Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018
Income Tax Disclosure [Abstract]
Discrete income tax benefit for vested stock awards	$ 22	$ 58

Amount of tax benefit for recognition of expense of award under share-based payment arrangement.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(i)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration