Accounting Policies - Calculation of Diluted Shares (Details) - shares shares in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accounting Policies [Abstract]
Shares used in computation of basic earnings per share	481	474	479	473
Total dilutive effect of outstanding stock awards	13	11	13	10
Shares used in computation of diluted earnings per share	494	485	492	483