Variable Interest Entities (Variable Interest Entity, Consolidated, Carrying Amount, Assets) (Details) - Variable Interest Entity, Not Primary Beneficiary [Member] - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Other Assets [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	$ 35.7	$ 22.8
Accounts Payable and Accrued Liabilities [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	24.3	14.0
Other Investments [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	13.0	12.3
Unfunded Loan Commitment [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	$ 22.4	$ 19.9