Other Comprehensive Income and Accumulated Other Comprehensive Income (Significant Reclassifications from AOCI) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Total revenues	$ 1,444.6	$ 1,203.3	$ 2,889.4	$ 2,343.7
Other income (expense)			(3.3)	4.1
(Loss) income before income taxes	(1,352.1)	499.5	(688.5)	1,041.3
Income tax provision	284.0	(39.7)	178.0	6.4
Net (loss) income	(1,068.1)	459.8	(510.5)	1,047.7
Unrealized Gains (Losses) from Hedging Activities | Reclassification out of Accumulated Other Comprehensive Income
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Total revenues	9.5	9.1	20.9	16.1
Other income (expense)	(10.0)	4.5	(14.6)	9.1
(Loss) income before income taxes	(0.5)	13.6	6.3	25.2
Income tax provision	0.2	(3.2)	(1.4)	(5.8)
Net (loss) income	$ (0.3)	$ 10.4	$ 4.9	$ 19.4