Stockholders' Equity (Schedule of Treasury Stock) (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended		98 Months Ended
		Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2016
Class of Stock [Line Items]
Shares repurchased		0	0	27,307,796
Average purchase price per share		$ 0.00	$ 0.00	$ 48.90
Cash paid for repurchased shares (in millions)		$ 0	$ 0	$ 1,335
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.