Earnings Per Share - Additional Information (Detail) - $ / shares shares in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Weighted Average
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of anti-dilutive securities (in shares)			5
Mandatory Convertible Notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of anti-dilutive securities (in shares)	39	39	26
Shares that would have been included in diluted earnings per share calculation (in shares)	30	28	26
Convertible Notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of anti-dilutive securities (in shares)	14	14
Shares that would have been included in diluted earnings per share calculation (in shares)	14	10	5
Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of anti-dilutive securities (in shares)	11	13	11
Shares that would have been included in diluted earnings per share calculation (in shares)	1	1	1
Weighted average exercise price of options (usd per share)	$ 33.32	$ 26.93	$ 38.25
Stock Awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of anti-dilutive securities (in shares)	7	8	7
Shares that would have been included in diluted earnings per share calculation (in shares)	5	4	4
Equity Unit Purchase Agreements
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of anti-dilutive securities (in shares)	3	10	9

Shares that would have been included in diluted earnings per share calculation.

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- Definition

The weighted average exercise price of stock options whose individual exercise prices were greater than the average market price of an entity's common stock during the period.

+ References

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- Definition

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

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- Definition

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.

+ References

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