Balance Sheet Accounts and Supplemental Disclosures - Inventories (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Long-term contracts at average cost	$ 551.9	$ 543.5
Progress payments	(368.2)	(388.5)
Total long-term contract inventories	183.7	155.0
Total other inventories	1.4	1.2
Inventories	185.1	156.2
General and administrative costs incurred	257.4	18.3
Cumulative amount of general and administrative costs in long-term contract inventories estimated	$ 21.1	$ 17.1