Investments (Schedule of Realized Gain (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Fixed Maturities Excluding Held-For-Sale Chaucer [Member]
Gain (Loss) on Investments [Line Items]
Proceeds from Sales	$ 60.1	$ 57.1
Gross Gains	1.0	0.2
Gross Losses	1.5	1.7
Fixed Maturities Held-For-Sale [Member]
Gain (Loss) on Investments [Line Items]
Proceeds from Sales	0.3	70.7
Gross Gains		0.4
Gross Losses		0.6
Fixed Maturities Including Held For Sale [Member]
Gain (Loss) on Investments [Line Items]
Proceeds from Sales	60.4	127.8
Gross Gains	1.0	0.6
Gross Losses	$ 1.5	$ 2.3