STATEMENT OF COMPREHENSIVE INCOME (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Statement of Comprehensive Income [Abstract]
Change in Net Unrealized Loss on Securities, Tax Expense (Benefit)	$ (248.8)	$ 71.7	$ (326.3)	$ 203.9
OCI, Liability for Future Policy Benefit, Gain (Loss), after REclassification Adjustment, Tax	454.8	(106.0)	520.8	(137.7)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification, Tax	(35.1)	5.9	(35.3)	1.7
Change in Foreign Currency Translation Adjustment, Tax Expense (Benefit)	(0.1)	0.1	(0.5)	(0.1)
Change in Unrecognized Pension and Postretirement Benefit costs, Tax Expense	$ (0.6)	$ (1.4)	$ (2.1)	$ (0.7)