Investments (Narrative) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021 USD ($) security	Mar. 31, 2020 USD ($)	Dec. 31, 2020 security
Schedule of Available-for-sale Securities [Line Items]
Gross gains on investments | $	$ 1.5	$ 20.4
Gross losses on investments | $	0.1	14.8
Proceeds from sale of investment securities | $	1.2	100.8
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Number of Positions [Abstract]
Other-than-temporary impairment | $	$ 0.0	$ 0.0
Number of securities sold | security	0
Debt Securities [Member]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Number of Positions [Abstract]
Number of debt securities with unrealized loss | security	90		81
Number of debt securities with unrealized loss, less than 12 months | security	49		64
Number of debt securities with unrealized loss, greater than 12 months | security	41		17