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Acquisitions and Dispositions of Businesses - Dispositions (Details) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2016 USD ($) disposal | Sep. 30, 2015 USD ($) disposal | Sep. 30, 2016 USD ($) disposal | Sep. 30, 2015 USD ($) disposal
Dispositions |  |  |  |
Gain on disposal of business | $ | $ 0 | $ 0 | $ 41 | $ 20
Disposal Group, Not Discontinued Operations [Member] |  |  |  |
Dispositions |  |  |  |
Number of dispositions | 0 | 1 | 4 | 3
Disposal Group, Not Discontinued Operations [Member] | Risk Solutions [Member] |  |  |  |
Dispositions |  |  |  |
Number of dispositions | 0 | 1 | 3 | 2
Disposal Group, Not Discontinued Operations [Member] | HR Solutions [Member] |  |  |  |
Dispositions |  |  |  |
Number of dispositions | 0 | 0 | 1 | 1

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- Definition Amount before tax of gain (loss) recognized on the sale or disposal of a disposal group. Excludes discontinued operations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=68055307&loc=d3e2443-110228 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=64862545&loc=d3e2941-110230 + Details
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