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Investments (Narrative) (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended	12 Months Ended
Investments (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Apr. 30, 2020
Investments [Abstract]
Equity method investments	$ 69.5	$ 69.5	$ 69.5	$ 69.1
Schedule of Investments [Line Items]
Investments in marketable equity securities	62.4	62.4	62.4	4.4
Purchase of additional interest in marketable equity securities				3.5
Realized gain (loss) on marketable securities	37.4
Unrealized gains on marketable equity securities		45.4
Investments in non-marketable equity securities	$ 35.8	35.8	35.8	61.8
Impairment related to partial write-down of equity method investment			$ 20.0	$ 20.2
Unrealized gain		$ 14.9
Reclassified from Non-marketable Security to Marketable Security [Member]
Schedule of Investments [Line Items]
Investments in marketable equity securities					$ 25.0