Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Statement of Comprehensive Income [Abstract]
Net Income	$ 896.1	$ 331.8	$ 1,110.8	$ 666.4
Other Comprehensive Income (Loss) (Net of Tax and Reclassifications)
Net Unrealized Gains (Losses) on Available for Sale Debt Securities	43.4	(42.0)	256.8	138.2
Net Unrealized Gains (Losses) on Cash Flow Hedges	(0.1)	(0.6)	(0.8)	(0.7)
Net Foreign Currency Adjustments	7.0	1.9	11.6	24.6
Net Pension and Other Postretirement Benefit Adjustments	2.3	1.0	5.3	1.2
Net Change	52.6	(39.7)	272.9	163.3
Comprehensive Income (Loss)	$ 948.7	$ 292.1	$ 1,383.7	$ 829.7