Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Statement of Comprehensive Income [Abstract]
Net Income	$ 392.0	$ 214.7
Other Comprehensive Income (Loss) (Net of Tax and Reclassifications)
Net Unrealized Gains (Losses) on Available for Sale Debt Securities	71.0	213.4
Net Unrealized Gains (Losses) on Cash Flow Hedges	(0.5)	(0.7)
Net Foreign Currency Adjustments	4.7	4.6
Net Pension and Other Postretirement Benefit Adjustments	(0.7)	3.0
Other Comprehensive Income (Loss)	74.5	220.3
Comprehensive Income (Loss)	$ 466.5	$ 435.0