Income Taxes - Valuation Allowances (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Valuation Allowance [Line Items]
Valuation allowance, deferred tax assets	$ 5.0	$ 7.1
Increase (decrease) in valuation allowance	(2.1)	(3.6)	$ (0.4)
Tax valuation allowance allocated to Net income (loss)
Valuation Allowance [Line Items]
Valuation allowance, deferred tax assets	124.3	126.4
Tax valuation allowance allocated to Other comprehensive income
Valuation Allowance [Line Items]
Valuation allowance, deferred tax assets	$ (119.3)	$ (119.3)