Balance Sheet Accounts and Supplemental Disclosures - Other Current Assets, net (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Other Current Assets [Line Items]
Prepaid expenses	$ 16.5	$ 11.9
Receivables, net	17.8	10.6
Recoverable from the U.S. government for competitive improvement program obligations (see Note 10)	7.6	9.1
Income tax receivable	26.8	1.6
Other	5.6	8.4
Other current assets, net	91.7	69.2
UTC [Member]
Other Current Assets [Line Items]
Receivables, net	5.5	15.7
Business Integration Costs [Member]
Other Current Assets [Line Items]
Recoverable from the U.S. government for Rocketdyne Business integration costs (see Note 3(f))	$ 11.9	$ 11.9