Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Statement of Comprehensive Income [Abstract]
Net Income	$ 464.9	$ 327.8	$ 1,575.7	$ 994.2
Other Comprehensive Income (Loss) (Net of Tax and Reclassifications)
Net Unrealized Gains (Losses) on Available for Sale Debt Securities	63.9	32.3	320.7	170.5
Net Unrealized Gains (Losses) on Cash Flow Hedges	0.3	(0.4)	(0.5)	(1.1)
Net Foreign Currency Adjustments	18.9	9.6	30.5	34.2
Net Pension and Other Postretirement Benefit Adjustments	2.4	1.0	7.7	2.2
Other Comprehensive Income (Loss)	85.5	42.5	358.4	205.8
Comprehensive Income (Loss)	$ 550.4	$ 370.3	$ 1,934.1	$ 1,200.0