Stockholders' Equity (Schedule of Treasury Stock) (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended					83 Months Ended
	Dec. 31, 2014	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2014		Oct. 23, 2014	Feb. 06, 2014	Oct. 18, 2012	Apr. 25, 2011	Oct. 23, 2008	Feb. 08, 2008
Class of Stock [Line Items]
Share repurchase plan, authorized repurchase amount	$ 1,366					$ 1,366		$ 301	$ 172	$ 264	$ 129	$ 100	$ 400
Shares repurchased	4,338,488	3,186,180	[1]	1,059,719	[1]	20,667,195	[2]
Average purchase price per share	$ 57.61	$ 51.38		$ 42.44		$ 44.27
Amount spent on repurchased shares (in millions)	$ 250	$ 164		$ 45		$ 915
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 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. Restricted stock awards are considered outstanding at the time of issuance. Accordingly, 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. Restricted stock awards are considered outstanding at the time of issuance. Accordingly, the shares withheld are treated as treasury shares.