Quarterly Results of Operations (Unaudited) (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Mar. 31, 2020
Effect of Fourth Quarter Events [Line Items]
CARES Act, tax benefit					$ 79.3
Hurricane Ida
Effect of Fourth Quarter Events [Line Items]
Impact after-tax of reportable catastrophes	$ 78.0	$ 34.5
Hurricane Laura
Effect of Fourth Quarter Events [Line Items]
Impact after-tax of reportable catastrophes			$ 27.3	$ 87.0