Stockholders' Equity (Schedule of Treasury Stock) (Details) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended				12 Months Ended					71 Months Ended
	Oct. 31, 2012	Apr. 30, 2011	Oct. 31, 2008	Feb. 29, 2008	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011	Dec. 31, 2013
Class of Stock [Line Items]
Share repurchase plan, authorized repurchase amount	$ 264	$ 129	$ 100	$ 400	$ 893
Shares repurchased					3,186,180	[1]	1,059,719	[1]	652,016	16,328,707	[2]
Average purchase price per share					$ 51.38		$ 42.44		$ 46.99	$ 40.72
Amount spent on repurchased shares					$ 164		$ 45		$ 31	$ 665
Restricted Stock [Member]
Class of Stock [Line Items]
Shares withheld, tax withholding					6,021		5,823			11,844

[1] The years ended December 31, 2013 and 2012 exclude 6,021 shares and 5,823 shares, respectively, withheld from an executive officer to cover statutory minimum withholding requirements for personal income taxes related to the vesting of restricted stock awards. Restricted stock awards are considered outstanding at the time of issuance and therefore, the shares withheld are treated as treasury shares.

[2] 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 awards.