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EMPLOYEE BENEFIT PLANS - Narrative (FY) (Details) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Sep. 30, 2018
Defined Benefit Plans And Other Postretirement Benefit Plans [Line Items] |  |  |
Number of shares held on behalf of participants (in shares) | 495,274 | 551,482 |
Market value of the shares held on behalf of participants | $ 40.3 | $ 45.8 |
United States | Defined Benefit Pension Plans |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans [Line Items] |  |  |
Aggregate accumulated benefit obligation | 43.3 | 44.5 |
Contribution to the plan | $ 0.0 |  |
United States | Defined Benefit Pension Plans | Equity security funds |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans [Line Items] |  |  |
Target asset allocation (as a percent) | 55.00% |  |
United States | Defined Benefit Pension Plans | Debt security funds and other |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans [Line Items] |  |  |
Target asset allocation (as a percent) | 45.00% |  |
United States | Other Postretirement Benefits Plans |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans [Line Items] |  |  |
Assumed health care cost trend rate, initial rate (as a percent) | 6.30% |  |
Assumed health care cost trend rate, ultimate rate (as a percent) | 4.50% |  |
Effect of 1% point increase on service and interest cost components (less than) | $ 0.1 |  |
Effect of 1% point increase on accumulated postretirement benefit obligation | 0.1 |  |
Effect of 1% point decrease on service and interest cost components (less than) | 0.1 |  |
Effect of 1% point decrease on accumulated postretirement benefit obligation | 0.1 |  |
Foreign Plan | Defined Benefit Pension Plans |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans [Line Items] |  |  |
Aggregate accumulated benefit obligation | 344.3 | $ 312.2 |
Contribution to the plan | $ 7.3 |  | $ 7.3
Foreign Plan | Defined Benefit Pension Plans | Equity security funds |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans [Line Items] |  |  |
Target asset allocation (as a percent) | 30.00% |  |
Foreign Plan | Defined Benefit Pension Plans | Debt security funds and other |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans [Line Items] |  |  |
Target asset allocation (as a percent) | 40.00% |  |
Foreign Plan | Defined Benefit Pension Plans | Other Investments |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans [Line Items] |  |  |
Target asset allocation (as a percent) | 30.00% |  |
Foreign Plan | Other Postretirement Benefits Plans |  |  |
Defined Benefit Plans And Other Postretirement Benefit Plans [Line Items] |  |  |
Assumed health care cost trend rate, initial rate (as a percent) | 6.23% |  |
Assumed health care cost trend rate, ultimate rate (as a percent) | 4.50% |  |
Effect of 1% point increase on service and interest cost components (less than) | $ 0.1 |  |
Effect of 1% point increase on accumulated postretirement benefit obligation | 0.3 |  |
Effect of 1% point decrease on service and interest cost components (less than) | 0.1 |  |
Effect of 1% point decrease on accumulated postretirement benefit obligation | $ 0.3 |  |

X
- Definition Amount of actuarial present value of benefits attributed to employee service rendered, excluding assumptions about future compensation level. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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