Intangible Assets (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 7	$ 7
Finite-lived intangible assets, future amortization expense, four year estimate, minimum	21
Finite-lived intangible assets, future amortization expense, four year estimate, maximum	$ 26
Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Estimated useful lives (in years)	1 year
Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Estimated useful lives (in years)	20 years