Stockholders' Equity (Schedule of Treasury Stock) (Details) - USD ($) $ / shares in Units, $ in Millions		6 Months Ended		137 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019
Class of Stock [Line Items]
Shares repurchased		4,890,155	888,383	52,602,866
Average purchase price per share		$ 102.25	$ 112.56	$ 69.44
Shares repurchased (in $ millions)		$ 500	$ 100	$ 3,653
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.