Financial Derivatives (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Mar. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Derivative [Line Items]
Written credit derivative spread threshold		20.00%	20.00%
Upfront points on written credit derivative in excess of threshold			57.0
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	$ (3.3)	$ (2.1)
Minimum
Derivative [Line Items]
Spread on written credit derivatives		10.01%	1.09%
Upfront points on written credit derivative in excess of threshold		57.0
Maximum
Derivative [Line Items]
Spread on written credit derivatives		100.11%	44.00%
Upfront points on written credit derivative in excess of threshold		85.2