Fair Value Disclosures - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Credit Risk Valuation Adjustment, Derivative Assets	$ 0.2	$ 0.2
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets and Liabilities, Fair Value Disclosure	$ 6,100.0	$ 5,500.0
Fair Value, Assets and Liabilities Fair Value as Percent of Total Assets	39.00%	38.00%
Fair Value, Assets and Liabilities, Fair Value as Percent of Total Financial Instruments Measured at Fair Value	69.00%	73.00%