Investments - Allowance for Loan Losses (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Collective valuation allowance for losses, beginning of period	$ 1.2	$ 1.1
Addition to (reduction of) allowance for losses	(0.1)	0.1
Collective valuation allowance for losses, end of period	$ 1.1	$ 1.2