Consolidated Statements of Comprehensive Income - USD ($) shares in Millions, $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Revenues
Net premiums earned		$ 14,894.3	$ 12,398.9	$ 42,891.8	$ 36,349.7
Investment income		510.2	333.6	1,384.3	868.2
Net realized gains (losses) on securities:
Net realized gains (losses) on security sales		(66.2)	(62.1)	38.6	430.0
Net holding period gains (losses) on securities		(80.5)	(152.1)	17.9	(2,262.9)
Net impairment losses recognized in earnings		(2.3)	(2.2)	(6.8)	(6.5)
Total net realized gains (losses) on securities		(149.0)	(216.4)	49.7	(1,839.4)
Fees and other revenues		223.7	181.4	656.6	531.9
Service revenues		81.4	82.7	234.9	230.5
Total revenues		15,560.6	12,780.2	45,217.3	36,140.9
Expenses
Losses and loss adjustment expenses		11,387.9	10,018.7	34,182.0	28,298.2
Policy acquisition costs		1,173.2	970.9	3,442.6	2,867.9
Other underwriting expenses		1,420.7	1,496.4	4,710.3	4,433.9
Investment expenses		7.2	5.8	18.8	17.4
Service expenses		91.7	82.8	264.6	221.5
Interest expense		69.7	63.1	198.7	180.4
Goodwill impairment		0.0	0.0	0.0	224.8
Total expenses		14,150.4	12,637.7	42,817.0	36,244.1
Net Income (Loss)
Income (loss) before income taxes		1,410.2	142.5	2,400.3	(103.2)
Provision for income taxes		288.9	18.4	485.7	1.7
Net income (loss)		1,121.3	124.1	1,914.6	(104.9)
Other Comprehensive Income (Loss)
Total net unrealized gains (losses) on fixed-maturity securities		(388.6)	(920.3)	(241.0)	(3,170.0)
Net unrealized losses on forecasted transactions		0.2	0.1	0.4	0.3
Foreign currency translation adjustment		0.0	(0.7)	0.2	(0.9)
Other comprehensive income (loss)		(388.4)	(920.9)	(240.4)	(3,170.6)
Comprehensive income (loss)		732.9	(796.8)	1,674.2	(3,275.5)
Computation of Earnings Per Common Share
Net income (loss)		1,121.3	124.1	1,914.6	(104.9)
Less: Preferred share dividends	[1]	10.4	6.7	27.2	20.1
Net income (loss) available to common shareholders		$ 1,110.9	$ 117.4	$ 1,887.4	$ (125.0)
Average common shares outstanding - Basic (in shares)		584.8	584.5	584.9	584.4
Net effect of dilutive stock-based compensation (in shares)		2.7	2.6	2.6	2.7
Total average equivalent common shares - Diluted (in shares)		587.5	587.1	587.5	587.1
Basic: Earnings per common shares (in dollars per share)		$ 1.90	$ 0.20	$ 3.23	$ (0.21)
Diluted: Earnings per common share (in dollars per share)		$ 1.89	$ 0.20	$ 3.21	$ (0.21)

[1] Changed to a floating dividend rate in March 2023. See Note 1 – Basis of Reporting and Accounting for further discussion.