Equity - Capital Requirements (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Equity [Abstract]
Capital Requirements, Minimum Capital, Percentage of Aggregate On-Balance Sheet Assets Included In Core Capital	2.75%
Capital Requirements, Minimum Capital, Percentage of Aggregate Off-Balance Sheet Assets Included In Core Capital	0.75%
Capital Requirements, Critical Capital, Percentage of Core Capital of Total Minimum Capital	50.00%
Minimum Capital Required	$ 462.1	$ 421.3
Core Capital Level	564.5	766.3
Excess Core Capital Level	$ 102.4	$ 345.0