Stockholders' Equity (Schedule of Treasury Stock) (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended		134 Months Ended
		Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019
Class of Stock [Line Items]
Shares repurchased		1,972,291	0	49,685,002
Average purchase price per share		$ 101.41	$ 0.00	$ 67.48
Shares repurchased (in $ millions)		$ 200	$ 0	$ 3,353
Aggregate Board of Directors repurchase authorizations (in $ millions)	[1]	$ 0	$ 0	$ 3,866

[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.