Balance Sheet Accounts and Supplemental Disclosures - Other Noncurrent Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Conditional asset retirement obligations	$ 44.0	$ 30.6
Pension benefits, non-qualified	17.6	17.5
Deferred compensation	29.4	19.8
Deferred revenue	12.7	13.3
Postretirement medical and life insurance benefits	32.7	37.4
Competitive improvement program obligations	18.4	1.3
Uncertain income tax positions	2.8	28.4
Other	13.5	13.1
Other noncurrent liabilities	$ 171.1	$ 161.4

Defined Benefit Pension Plan Nonqualified

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Other Components Of Other Noncurrent Liabilities

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Postretirement Medical Benefits Non Current

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Supplemental Unemployment Benefits, Noncurrent

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Noncurrent portion of the carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

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Aggregate carrying value as of the balance sheet date of the liabilities for all deferred compensation arrangements payable beyond one year (or the operating cycle, if longer).

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The noncurrent portion of deferred revenue amount as of balance sheet date. Deferred revenue is a liability related to a revenue producing activity for which revenue has not yet been recognized, and is not expected to be recognized in the next twelve months. Generally, an entity records deferred revenue when it receives consideration from a customer before achieving certain criteria that must be met for revenue to be recognized in conformity with GAAP.

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Amount recognized for uncertainty in income taxes classified as noncurrent.

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Amount of liabilities classified as other, due after one year or the normal operating cycle, if longer.

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