Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Statement of Comprehensive Income [Abstract]
Net Income	$ 2,031.1	$ 1,107.3	$ 1,336.0
Other Comprehensive Income (Loss) (Net of Tax and Reclassifications)
Net Unrealized Gains (Losses) on Available for Sale Debt Securities	325.8	443.7	(1,474.7)
Net Unrealized Gains (Losses) on Cash Flow Hedges	(0.2)	(0.4)	3.6
Net Foreign Currency Adjustments	29.5	39.0	9.4
Net Pension and Other Postretirement Benefit Adjustments	(31.2)	(51.0)	(71.9)
Net Change	323.9	431.3	(1,533.6)
Comprehensive Income (Loss)	$ 2,355.0	$ 1,538.6	$ (197.6)