Stockholders' Equity - Earnings per Share (Details) - shares shares in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Equity [Abstract]
As reported shares (in shares)	1,014.0	998.0	1,012.0	996.0
Effect of stock-based compensation (in shares)	0.0	7.0	5.0	7.0
Diluted shares (in shares)	1,014.0	1,005.0	1,017.0	1,003.0
Stock options and performance share award units that were not included in the diluted earnings per share calculation (in shares)	5.3	0.0	0.0	0.0