Accounting Policies - Calculation of Diluted Shares (Details) - shares shares in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Accounting Policies [Abstract]
Shares used in computation of basic earnings per share	486	479	485	478
Total dilutive effect of outstanding stock awards	14	13	14	13
Shares used in computation of diluted earnings per share	500	492	499	491