Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 115.5	$ (12.0)
Changes in net unrealized gains (losses) on investment securities:
Having no credit losses recognized in the Consolidated Statements of Income (Loss)	(33.9)	93.3
Having credit losses recognized in the Consolidated Statements of Income (Loss)	(0.2)	1.0
Total available-for-sale securities	(34.1)	94.3
Pension and postretirement benefits:
Net change in net actuarial loss	1.4	1.6
Long-duration insurance contracts:
Net change in market risk	1.0	(2.1)
Total other comprehensive income (loss), net of tax	(31.7)	93.8
Comprehensive income	$ 83.8	$ 81.8