Balance Sheet Accounts and Supplemental Disclosures - Estimated Amounts to be Amortized from Other Comprehensive Loss (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Pension Benefits
Accumulated Other Comprehensive Income (Loss) [Line Items]
Actuarial losses (gains), net	$ 70.7
Prior service costs (credits), net	0.1
Total	$ 70.8
Medical and Life Insurance Benefits
Accumulated Other Comprehensive Income (Loss) [Line Items]
Actuarial losses (gains), net		$ (3.7)
Prior service costs (credits), net		(0.2)
Total		$ (3.9)

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of cost (credit) included in accumulated other comprehensive (income) loss expected to be recognized in net periodic benefit cost (credit) for fiscal year following most recent annual statement of financial position.

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

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