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Acquisitions and Investments - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) Acquisition	Dec. 31, 2016 USD ($) Acquisition	Dec. 31, 2015 USD ($) Acquisition
Acquired Finite-Lived Intangible Assets [Line Items]
Aggregate cash investment of acquisitions	$ 86	$ 230	$ 86
Goodwill	$ 6,227	$ 6,067	$ 6,980
All Other Acquisitions [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Acquisitions completed | Acquisition	8	10	7
Aggregate cash investment of acquisitions	$ 86	$ 230	$ 86
Intangible assets	61	24	13
Goodwill	$ 89	74	$ 51
Business acquisition Nov stock issued		$ 18

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- Definition

Business Acquisition Purchase Price Allocation Intangible Assets

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

Value of equity interests (such as common shares, preferred shares, or partnership interest) issued or issuable to acquire the entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)(4)
-URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6927-128479

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Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
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-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

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-Name Accounting Standards Codification
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-Section 45
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-URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975

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The number of businesses acquired by the entity during the period.

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The cash outflow associated with the acquisition of a business, net of the cash acquired from the purchase.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
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