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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

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- Definition

Amount of decrease in accumulated postretirement benefit obligation from one-percentage-point decrease in assumed health care cost trend rate.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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Amount of decrease in service and interest cost components of net periodic postretirement benefit cost from one-percentage-point decrease in assumed health care cost trend rate.

+ 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 (m)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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+ 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 (m)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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+ 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 (m)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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Amount of contributions expected to be received by defined benefit plan from employer in fiscal year. Excludes contributions paid by employer in current fiscal year.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2709-114920

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- Definition

Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

+ 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 (d)(5)(i)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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Ultimate trend rate for health care cost for defined benefit postretirement plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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The trend rate for health care cost associated with the defined benefits plan.

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Defined Contribution Plan, Market value of the shares held on behalf of participants

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Defined Contribution Plan, Number of shares held on behalf of participants.

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