Financial Derivatives (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Derivative [Line Items]
Written credit derivative spread threshold	20.00%	20.00%
Credit Default Swap, Selling Protection [Member]
Derivative [Line Items]
Credit risk derivative in excess of threshold, at fair value, net	$ (0.1)	$ (0.1)
Total net up-front payments received	$ (2.0)	$ (2.0)
Minimum
Derivative [Line Items]
Spread on written credit derivatives	2.81%	4.00%
Upfront points on written credit derivative in excess of threshold	56.2	56.2
Maximum
Derivative [Line Items]
Spread on written credit derivatives	26.44%	27.48%
Upfront points on written credit derivative in excess of threshold	85.2	85.2