Investment Securities (Schedule of Interest and Dividend Income) (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Investments Debt And Equity Securities [Abstract]
Interest income - debt securities	$ 39.2	$ 48.0
Interest income - interest-bearing cash	5.6	14.5
Dividends - equity securities	1.2	2.7
Total interest and dividends	$ 46.0	$ 65.2

Amount of interest income, amortization of premium and accretion of discount on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale); classified as operating.

No definition available.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration