Investments - Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at January 1	$ 58.2	$ 71.7	$ 50.4
Charged to costs and expenses	24.4	22.8	54.9
Charged to other accounts (1)	(0.9)	(4.1)	1.4
Deductions (2)	(39.5)	(32.2)	(35.0)
Balance at December 31	$ 42.2	$ 58.2	$ 71.7