Balance Sheet Accounts - Schedule of Other Noncurrent Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Conditional asset retirement obligations	$ 44.5	$ 44.0
Pension benefits, non-qualified	17.4	17.6
Deferred compensation	27.6	29.4
Deferred revenue	12.5	12.7
Postretirement medical and life insurance benefits	32.0	32.7
Competitive improvement program obligations	15.6	18.4
Uncertain income tax positions	4.9	2.8
Other	15.9	13.5
Other noncurrent liabilities	$ 170.4	$ 171.1