Summary of Significant Accounting Policies - Other (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Relocation properties, aggregate selling price	$ 81	$ 123	$ 170
Advertising expense	166	164	156
Restricted cash	$ 9	$ 7
Impairment analysis of goodwill - evaluation of the effect of reducing fair value for each reporting unit by a specified percentage	10.00%	10.00%	10.00%
Minimum [Member]
Consolidated subsidiary, parent's ownership percentage	50.00%
Maximum [Member]
Highly-liquid investments, remaining maturity	3 months

- Definition

The carrying amounts of cash and cash equivalent items which are restricted as to withdrawal or usage. Restrictions may include legally restricted deposits held as compensating balances against short-term borrowing arrangements, contracts entered into with others, or entity statements of intention with regard to particular deposits; however, time deposits and short-term certificates of deposit are not generally included in legally restricted deposits. Excludes compensating balance arrangements that are not agreements which legally restrict the use of cash amounts shown on the balance sheet. For a classified balance sheet represents the current portion only (the noncurrent portion has a separate concept); there is a separate and distinct element for unclassified presentations.

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