Stockholders' Equity (Schedule of Treasury Stock) (Details) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended				6 Months Ended			65 Months Ended
	Oct. 31, 2012	Apr. 30, 2011	Oct. 31, 2008	Feb. 29, 2008	Jun. 30, 2013		Jun. 30, 2012	Jun. 30, 2013
Class of Stock [Line Items]
Share repurchase plan, authorized repurchase amount	$ 264	$ 129	$ 100	$ 400				$ 893
Shares repurchased					137,692	[1]	636,710	13,280,219	[2]
Average purchase price per share					$ 46.24		$ 45.09	$ 38.23
Amount spent on repurchased shares					$ 6		$ 28	$ 507
Restricted Stock [Member]
Class of Stock [Line Items]
Shares withheld, tax withholding					6,021			11,844

[1] Excludes 6,021 shares withheld from employee to cover statutory minimum withholding requirements for personal income taxes related to the vesting of restricted stock. Restricted stock is considered outstanding at the time of issuance and therefore, the shares withheld are treated as treasury shares.

[2] Excludes 11,844 shares withheld from employee to cover statutory minimum withholding requirements for personal income taxes related to the vesting of restricted stock. Restricted stock is considered outstanding at the time of issuance and therefore, the shares withheld are treated as treasury shares.