Cash and Cash Equivalents (Details) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2013 USD ($) Y M	Mar. 31, 2013 GBP (£) Y M	Dec. 31, 2012 USD ($)
Cash, Cash Equivalents, and Short-term Investments [Abstract]
Short-term investment, minimum maturity period (in months)	3	3
Short-term investment, maximum maturity period (in years)	1	1
Operating funds in U.K.	$ 117	£ 77	$ 124
Cash and cash equivalents, restricted	$ 153		$ 76

- 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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