Description of Business and Accounting Policies - Calculation of Diluted Shares (Details) - shares shares in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Shares used in computation of basic earnings per share	490	488	486	484	483	481	479	477	487	480	474
Total dilutive effect of outstanding stock awards									13	13	10
Shares used in computation of diluted earnings per share	501	501	500	498	496	494	492	490	500	493	484