Common Stock and Stock Compensation - Shares Used to Compute Diluted Earnings Per Share (Details) - shares shares in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings per share (EPS) —
As reported shares	910	897	877
Effect of options	4	4	4
Diluted shares	914	901	881