Summary of Accounting Policies - Internal Use Software Assets (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Finite-Lived Intangible Assets [Line Items]
Capitalized software development costs, net of amortization	$ 55	$ 58
Amortization of software development costs	$ 15	$ 15	$ 18
Minimum | Software Development [Member]
Finite-Lived Intangible Assets [Line Items]
Finite useful life of intangible assets, Maximum	3 years
Maximum | Software Development [Member]
Finite-Lived Intangible Assets [Line Items]
Finite useful life of intangible assets, Maximum	12 years