Stockholders' Equity (Schedule of Treasury Stock) (Details) - USD ($) $ / shares in Units, $ in Millions		6 Months Ended			89 Months Ended
		Jun. 30, 2015		Jun. 30, 2014	Jun. 30, 2015
Class of Stock [Line Items]
Shares repurchased		0	[1]	1,870,297	20,667,195	[2]
Average purchase price per share		$ 0.00		$ 55.13	$ 44.27
Cash paid for repurchased shares (in millions)		$ 0		$ 103	$ 915
Aggregate Board of Directors repurchase authorizations (in millions)	[3]	$ 0		$ 172	$ 1,366
Restricted Stock [Member]
Class of Stock [Line Items]
Shares withheld, tax withholding		9,264			21,108

[1] Excludes 9,264 shares withheld from an executive officer to cover statutory minimum withholding requirements for personal income taxes related to the vesting of restricted stock. Restricted stock awards are considered outstanding at the time of issuance. Accordingly, the shares withheld are treated as treasury shares.

[2] Excludes 21,108 shares withheld from an executive officer to cover statutory minimum withholding requirements for personal income taxes related to the vesting of restricted stock. Restricted stock awards are considered outstanding at the time of issuance. Accordingly, the shares withheld are treated as treasury shares.

[3] 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.