Balance Sheet Accounts - Schedule of Other Noncurrent Assets, net (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Recoverable from the U.S. government for conditional asset retirement obligations	$ 19.9	$ 20.3
Recoverable from the U.S. government for restructuring costs	18.5	12.8
Recoverable from the U.S. government for acquisition related integration costs	7.9	10.9
Recoverable from the U.S. government for competitive improvement program obligations	0.0	1.3
Deferred financing costs	3.2	3.4
Grantor trusts	17.9	16.6
Income taxes receivable	10.8	10.8
Notes receivable, net	9.0	9.0
Other	4.9	5.1
Other noncurrent assets, net	$ 92.1	$ 90.2