Financial Derivatives (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Credit Default Swap, Selling Protection [Member]
Derivative [Line Items]
Total net up-front payments received	$ 136.0	$ 137.8
Minimum [Member]
Derivative [Line Items]
Low Range Of Spread On Written Credit Derivatives	0.185%	0.195%
Maximum [Member]
Derivative [Line Items]
Low Range Of Spread On Written Credit Derivatives	36.671%	46.287%