Income Tax (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Provision for income taxes
Current tax expense	$ 2.5	$ 3.1	$ 9.0
Deferred tax expense	2.1	22.6	67.4
Income Tax Expense (Benefit)	$ 4.6	$ 25.7	$ 76.4