Accounting Policies and Supplemental Disclosures - Calculation of Diluted Shares (Details) - shares shares in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Accounting Policies [Abstract]
Shares used in computation of basic earnings per share (in shares)	507	501	505	500
Total dilutive effect of outstanding stock awards (in shares)	8	11	9	9
Shares used in computation of diluted earnings per share (in shares)	515	512	514	509