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Income Taxes - Summary of Income Tax Rate (Parenthetical) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Income Taxes [Line Items]
Provisional net increase (decrease) recognized in income tax expense	$ 11	$ (23)

X

- Definition

Income Taxes [Line Items]

+ References

No definition available.

+ Details

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- Definition

Amount of reasonable estimate for income tax expense (benefit) for which accounting for tax effect is incomplete pursuant to Tax Cuts and Jobs Act.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 2A
-Subparagraph (SAB Topic 5.EE.Q2(b))
-URI http://asc.fasb.org/extlink&oid=116825942&loc=SL116722634-122817

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