Balance Sheet Accounts - Schedule of Other Current Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accrued compensation and employee benefits	$ 88.3	$ 113.4
Competitive improvement program obligations	14.1	15.0
Income taxes payable	127.7	0.8
Postretirement medical and life insurance benefits	4.8	4.8
Interest payable	2.3	0.6
Other program liabilities	15.6	6.6
Other	14.8	15.7
Other current liabilities	267.6	156.9
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification of other current liabilities to contract liabilities	267.6	156.9
Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Expected a decrease in income tax payable upon IRS consent	105.0
Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Expected a decrease in income tax payable upon IRS consent	$ 115.0
Contract liabilities
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Other current liabilities		39.0
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification of other current liabilities to contract liabilities		$ 39.0