Stockholders' Equity (Schedule of Treasury Stock) (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended				86 Months Ended
	Mar. 31, 2015		Mar. 31, 2014		Mar. 31, 2015
Class of Stock [Line Items]
Shares repurchased	0		1,035,374		20,667,195	[1]
Average purchase price per share	$ 0.00		$ 51.30		$ 44.27
Cash paid for repurchased shares (in millions)	$ 0		$ 53		$ 915
Aggregate Board of Directors repurchase authorizations (in millions)	$ 0	[2]	$ 172	[2]	$ 1,366	[2]
Restricted Stock [Member]
Class of Stock [Line Items]
Shares withheld, tax withholding					11,844

[1] Excludes 11,844 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] 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.