Investment Securities - Investment Holding Common Equities/ Other Investments (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Common equity securities
Debt and Equity Securities, FV-NI [Line Items]
Cost or Amortized Cost	$ 124.2	$ 553.3
Gross Unrealized Gains	16.5	130.6
Gross Unrealized Losses	0.0	0.0
Net Foreign Currency Losses	0.0	0.0
Common equity securities, at fair value	140.7	683.9
Other long-term investments
Debt and Equity Securities, FV-NI [Line Items]
Cost or Amortized Cost	696.4	667.4
Gross Unrealized Gains	552.4	255.2
Gross Unrealized Losses	(76.1)	(64.1)
Net Foreign Currency Losses	(1.5)	(2.2)
Common equity securities, at fair value	$ 1,171.2	$ 856.3