Subsequent Event - Additional Information (Detail) - USD ($) $ in Millions	2 Months Ended	12 Months Ended
Mar. 01, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash consideration received in lieu of cancellation		$ 1,831	$ 1,271
Subsequent Event [Member]
Cancellation of common shares	3,216,363
Stock-based compensation awards, common shares	76,119
Cash consideration received in lieu of cancellation	$ 168

The cash outflow to reacquire common stock during the period.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (a)
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The number of shares purchased on the open market during the period for issuance to employees under the plan.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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- Definition

Number of shares that have been repurchased during the period and have not been retired and are not held in treasury. Some state laws may govern the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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