Stockholders' Equity - Earnings per Share (Details) - shares shares in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Equity [Abstract]
As reported shares (in shares)	1,011	993
Effect of options and performance share award units (in shares)	5	7
Diluted shares (in shares)	1,016	1,000
Stock options and performance share award units that were not included in the diluted earnings per share calculation (in shares)	0	0