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Acquisition and Divestitures (Schedule Of Intangible Assets) (Details) (USD $) In Millions, unless otherwise specified |  | 9 Months Ended | 12 Months Ended | 9 Months Ended | 12 Months Ended | 9 Months Ended | 12 Months Ended |  |  |  |  |  |  | 9 Months Ended |  | 9 Months Ended |  | 9 Months Ended | 0 Months Ended | 9 Months Ended | 0 Months Ended | 9 Months Ended | 0 Months Ended | 9 Months Ended
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May 31, 2012 | Sep. 30, 2013 Technology [Member] | Dec. 31, 2012 Technology [Member] | Sep. 30, 2013 Customer relationships [Member] | Dec. 31, 2012 Customer relationships [Member] | Sep. 30, 2013 Other [Member] | Dec. 31, 2012 Other [Member] | Dec. 31, 2012 NOS Clearing [Member] | Jul. 31, 2012 NOS Clearing [Member] | Dec. 31, 2012 BWise [Member] | May 31, 2012 BWise [Member] | May 31, 2012 BWise [Member] Technology [Member] | May 31, 2012 BWise [Member] Customer relationships [Member] | Sep. 30, 2013 eSpeed [Member] | Jun. 28, 2013 eSpeed [Member] | Sep. 30, 2013 eSpeed [Member] Trade Names [Member] | Sep. 30, 2013 eSpeed [Member] Technology [Member] | Jun. 28, 2013 eSpeed [Member] Technology [Member] | Sep. 30, 2013 eSpeed [Member] Customer relationships [Member] | Jun. 28, 2013 eSpeed [Member] Customer relationships [Member] | Sep. 30, 2013 eSpeed [Member] Market Services [Member] Trade Names [Member] | Sep. 30, 2013 eSpeed [Member] Market Services [Member] Technology [Member] | Sep. 30, 2013 eSpeed [Member] Market Services [Member] Customer relationships [Member] | Sep. 30, 2013 eSpeed [Member] Information Services [Member] Trade Names [Member] | Sep. 30, 2013 eSpeed [Member] Information Services [Member] Technology [Member] | Sep. 30, 2013 eSpeed [Member] Information Services [Member] Customer relationships [Member] | May 31, 2013 TR Businesses [Member] | Sep. 30, 2013 TR Businesses [Member] | May 31, 2013 TR Businesses [Member] Technology [Member] | Sep. 30, 2013 TR Businesses [Member] Technology [Member] | May 31, 2013 TR Businesses [Member] Customer relationships [Member] | Sep. 30, 2013 TR Businesses [Member] Customer relationships [Member] | Sep. 30, 2013 Minimum [Member] TR Businesses [Member] Technology [Member] | Sep. 30, 2013 Minimum [Member] TR Businesses [Member] Customer relationships [Member] | Sep. 30, 2013 Maximum [Member] TR Businesses [Member] Technology [Member] | Sep. 30, 2013 Maximum [Member] TR Businesses [Member] Customer relationships [Member]
Finite Lived And Indefinite Lived Intangible Assets [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquired Finite Lived Intangible Assets Weighted Average Useful Life |  | 5 years | 5 years | 19 years | 21 years | 8 years | 8 years |  |  |  |  |  |  |  |  |  |  | 5 years |  | 13 years |  |  | 5 years | 13 years |  | 5 years | 13 years |  |  |  |  |  |  | 2 years | 9 years | 5 years | 14 years
Indefinite-lived Intangible Assets Acquired |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 578 |  |  |  |  | $ 528 |  |  | $ 50 |  |  |  |  |  |  |  |  |  |  |  |
Finite-lived Intangible Assets Acquired |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 16 |  | 121 |  |  | 14 | 105 |  | 2 | 16 | 91 | 91 | 2 | 2 | 89 | 89 |  |  |  |
Purchased Intangible Assets | $ 35 |  |  |  |  |  |  | $ 1 | [1] | $ 1 | $ 35 | $ 35 | $ 7 | $ 23 | $ 715 | $ 715 |  |  | $ 16 |  | $ 121 |  |  |  |  |  |  |  | $ 91 |  |  |  |  |  |  |  |
[1] | In the third quarter of 2012, we recognized a gain of $4 million on our acquisition of NOS Clearing, which is included in merger and strategic initiatives expense in the Condensed Consolidated Statements of Income.

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- Definition Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16265-109275 + Details
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- Definition The amount of identifiable intangible assets recognized as of the acquisition date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6910749&loc=d3e4845-128472 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 55 -Paragraph 37 -URI http://asc.fasb.org/extlink&oid=25498275&loc=d3e2207-128464 + Details
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