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Restructuring Costs (Restructuring Activities) (Details) - USD ($) $ in Millions | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2017 | Dec. 31, 2016
Restructuring Reserve [Roll Forward] |  |
Liability at beginning of period | $ 93 | $ 93
Amounts Accrued | 32 | 44
Cash Paid | (57) | (39)
Other | 1 | (5)
Liability at end of period | 69 | 93
Severance |  |
Restructuring Reserve [Roll Forward] |  |
Liability at beginning of period | 32 | 15
Amounts Accrued | 24 | 40
Cash Paid | (42) | (22)
Other | 0 | (1)
Liability at end of period | 14 | 32
Future rent under non-cancelable leases and other costs |  |
Restructuring Reserve [Roll Forward] |  |
Liability at beginning of period | 61 | 78
Amounts Accrued | 8 | 4
Cash Paid | (15) | (17)
Other | 1 | (4)
Liability at end of period | 55 | $ 61
Operating Segments | Risk and Insurance Services Segment | Acquisition Related |  |
Restructuring Reserve [Roll Forward] |  |
Amounts Accrued | 7 |
Operating Segments | Consulting Segment | Acquisition Related |  |
Restructuring Reserve [Roll Forward] |  |
Amounts Accrued | 18 |
Corporate | Acquisition Related |  |
Restructuring Reserve [Roll Forward] |  |
Amounts Accrued | $ 7 |

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- Definition Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 5.P.3) -URI http://asc.fasb.org/extlink&oid=27011515&loc=d3e140864-122747 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6394359&loc=d3e17939-110869 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SAB Topic 5.P.4(b)) -URI http://asc.fasb.org/extlink&oid=27011515&loc=d3e140904-122747 + Details
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- Definition Carrying amount (including both current and noncurrent portions of the accrual) as of the balance sheet date pertaining to a specified type of cost associated with exit from or disposal of business activities or restructuring pursuant to a duly authorized plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SAB TOPIC 5.P.4(b)) -URI http://asc.fasb.org/extlink&oid=27011515&loc=d3e140904-122747 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b)(2) -URI http://asc.fasb.org/extlink&oid=6394359&loc=d3e17939-110869 + Details
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