Business Combinations and Other Investment Activities - Additional Information (Detail) $ in Millions	12 Months Ended
Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) Business_Acquisitions	Dec. 31, 2015 USD ($) Business_Acquisitions Transaction
Business Acquisition
Business acquisitions and other investing activities, net	21	16	17
Series of Individually Immaterial Business Acquisitions
Business Acquisition
Number of businesses acquired \| Business_Acquisitions		1	2
Consideration transferred	$ 21	$ 16
Business acquisitions and other investing activities, net			17
Number of equity investments \| Transaction			2
Number of business acquisitions			85
Other Nonoperating Income (Expense)
Business Acquisition
Gain (loss) on sale of equity investment			$ 57

Business Acquisitions And Other Investing Activities Net.

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Number of Business Acquisitions and Other Equity Investments

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Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 30
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=6911251&loc=d3e6578-128477

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6927-128479

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 30
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=6911251&loc=d3e6613-128477

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Amount of gain (loss) on sale or disposal of an equity method investment.

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