Cash and Cash Equivalents and Short-term Investments (Details) £ in Millions, $ in Millions	9 Months Ended
Sep. 30, 2015 GBP (£)	Sep. 30, 2015 USD ($)	Dec. 31, 2014 GBP (£)	Dec. 31, 2014 USD ($)
Cash, Cash Equivalents, and Short-term Investments [Abstract]
Short-term investment, minimum maturity period (in excess of)	3 months
Short-term investment, maximum maturity period (less than)	1 year
Cash and cash equivalents and Short-term investments		$ 783.0		$ 768.0
Restricted cash		107.0		169.0
Operating funds in U.K.	£ 42.7	64.8	£ 42.0	65.3
Cash and cash equivalents, restricted		$ 42.0		$ 104.0

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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.1)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_RestrictedCashAndCashEquivalentsAtCarryingValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant