Stockholders' Equity (Schedule of Treasury Stock) (Details) - USD ($) $ / shares in Units, $ in Millions		6 Months Ended		101 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016
Class of Stock [Line Items]
Shares repurchased		2,821,140	0	30,128,936
Average purchase price per share		$ 70.89	$ 0.00	$ 50.96
Cash paid for repurchased shares (in millions)		$ 200	$ 0	$ 1,535
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.