Summary of Accounting Policies Summary of Accounting Policies (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2012	Jun. 30, 2012	Sep. 30, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Accounting Policies [Abstract]
Prior Period Reclassification Adjustment	$ 25	$ 30	$ 35		$ 29
Capitalized Software Development Costs [Abstract]
Capitalized Computer Software Additions				4	5
Capitalized Computer Software Amortization				10	10	8
Capitalized Software Development Costs For Software Sold To Customers				9	14
Deferred Costs, Leasing, Net [Abstract]
Amortization of Deferred Leasing Fees				13	19	27
Deferred Costs, Leasing, Net, Noncurrent				26	31
Marketing and Advertising Expense [Abstract]
Other Deferred Cost, Amortization Expense				30	34	39
Deferred Advertising Costs				$ 73	$ 84