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Earnings Per Share - Additional Information (Detail) - $ / shares shares in Millions | 12 Months Ended
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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

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