Balance Sheet Accounts - Schedule of Other Current Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accrued compensation and employee benefits	$ 104.2		$ 113.4
Competitive improvement program obligations	14.6		15.0
Income taxes payable	136.4		0.8
Postretirement medical and life insurance benefits	4.8		4.8
Other program liabilities	33.2		6.6
Other	19.8		16.3
Other current liabilities	313.0		156.9
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification of other current liabilities to contract liabilities	$ 313.0		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