Stockholders' Equity (Schedule of Treasury Stock) (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended		110 Months Ended
		Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017
Class of Stock [Line Items]
Shares repurchased		1,461,966	0	35,804,182
Average purchase price per share		$ 89.95	$ 0.00	$ 54.93
Shares repurchased (in $ millions)		$ 131	$ 0	$ 1,966
Aggregate Board of Directors repurchase authorizations (in $ millions)	[1]	$ 0	$ 0	$ 2,366

[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.