Intangible Assets - Narrative (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Amortizable Intangible Assets [Line Items]
Acquired amortizable intangible assets, amount	$ 155
Goodwill added during period	222	30
Amortization expense	32	17	13
Finite-lived intangible assets, future amortization expense, four year estimate, minimum	21
Finite-lived intangible assets, future amortization expense, four year estimate, maximum	$ 27
Minimum
Amortizable Intangible Assets [Line Items]
Estimated useful life	1 year
Maximum
Amortizable Intangible Assets [Line Items]
Estimated useful life	20 years