Pension and Other Retiree Benefits (Effect of One Percent Change in Assumed Health Care Rate) (Details) - Post-retirement $ in Millions	12 Months Ended
Dec. 31, 2017 USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Effect of one percentage point increase on total of service and interest cost	$ 0.0
Effect of one percentage point decrease on total of service and interest cost	0.0
Effect of one percentage point increase on post-retirement benefit obligation	0.5
Effect of one percentage point decrease on post-retirement benefit obligation	$ (0.4)

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

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 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.

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

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