Derivative Financial Instruments (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Derivative [Line Items]
Gains or losses reclassified into earnings	$ 0.0	$ 0.0
Maximum length of time over which exposure was being hedged	23 months
Other comprehensive income (loss), cash flow hedge, gain (loss), before reclassification, after tax	$ 142.7	$ 28.6
Foreign Currency Denominate
Derivative [Line Items]
Estimated net gain (loss) to be reclassified into net income within the next twelve months relating to cash flow hedges	(2.6)
Foreign Currency Denominated Debt Securities
Derivative [Line Items]
Estimated net gain (loss) to be reclassified into net income within the next twelve months relating to cash flow hedges	16.9
Securities Sold Under Agreements to Repurchase
Derivative [Line Items]
Estimated net gain (loss) to be reclassified into net income within the next twelve months relating to cash flow hedges	$ (0.4)