Stockholders' Equity (Schedule of Treasury Stock) (Details) - USD ($) $ / shares in Units, $ in Millions		9 Months Ended		140 Months Ended
		Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019
Class of Stock [Line Items]
Shares repurchased		7,334,433	2,179,058	55,047,144
Average purchase price per share		$ 105.67	$ 114.73	$ 71.35
Shares repurchased (in $ millions)		$ 775	$ 250	$ 3,928
Aggregate Board of Directors repurchase authorizations (in $ millions)	[1]	$ 1,500	$ 0	$ 5,366

[1] These authorizations give management discretion in determining the timing and conditions under which shares may be repurchased. This repurchase program began in February 2008 and does not have an expiration date.