Other Assets and Liabilities - Other Non-Current Assets (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Schedule of Other Assets and Liabilities [Line Items]
Total	$ 64.5	$ 126.8
Other non-current assets
Schedule of Other Assets and Liabilities [Line Items]
Prepaid tax asset	0.0	56.2
Deferred financing costs	7.0	5.9
Long-term income tax receivables	14.0	2.1
Supply and Offtake receivable	32.7	46.3
Long-term derivative assets (see Note 16)	0.7	0.0
Other	$ 10.1	$ 16.3