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Earnings Per Share - Additional Information (Details) - shares shares in Millions | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016
Mandatory convertible preferred stock |  |
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] |  |
Shares that would have been included in diluted earnings per share calculation (in shares) | 30 | 28
Convertible notes |  |
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] |  |
Shares that would have been included in diluted earnings per share calculation (in shares) | 14 | 10
Stock Options |  |
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] |  |
Shares that would have been included in diluted earnings per share calculation (in shares) | 1 | 1
Stock awards |  |
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] |  |
Shares that would have been included in diluted earnings per share calculation (in shares) | 5 | 4

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