Earnings Per Share - Additional Information (Details) - shares shares in Millions	12 Months Ended
	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