Derivatives - Narrative (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Derivative [Line Items]
OTC Option Asset	$ 3.5	$ 3.8
OTC Option Liability	3.3	2.8
Derivative with Credit Risk Feature, Net	7.1	1.9
Derivative Instruments with Credit-Risk-Related Contingent Features [Member]
Derivative [Line Items]
Derivative, Collateral, Right to Reclaim Cash	54.0	$ 27.6
Derivative, Collateral, Obligation to Return Cash	$ 2.3