Unaudited Consolidated Statements of Income - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Revenues
Net premiums earned	$ 4,285	$ 3,970	$ 12,810	$ 10,957
Net investment income	408	399	1,191	1,090
Net realized gains (losses)	210	169	442	358
Other underwriting income	50	5	165	20
Equity in net income of investments accounted for using the equity method	134	171	349	437
Other income (loss)	22	8	38	30
Total revenues	5,109	4,722	14,995	12,892
Expenses
Losses and loss adjustment expenses	2,200	2,403	7,090	5,958
Acquisition expenses	786	681	2,374	1,921
Other operating expenses	478	353	1,405	1,062
Corporate expenses	49	49	156	143
Amortization of intangible assets	49	88	146	136
Interest expense	37	35	110	104
Net foreign exchange (gains) losses	7	63	122	31
Total expenses	3,606	3,672	11,403	9,355
Income (loss) before income taxes and income (loss) from operating affiliates	1,503	1,050	3,592	3,537
Income tax (expense) benefit	(215)	(98)	(550)	(296)
Income (loss) from operating affiliates	62	36	119	136
Net income (loss) available to Arch	1,350	988	3,161	3,377
Preferred dividends	(10)	(10)	(30)	(30)
Net income (loss) available to Arch common shareholders	$ 1,340	$ 978	$ 3,131	$ 3,347
Net income per common share and common share equivalent
Basic (per share)	$ 3.63	$ 2.62	$ 8.43	$ 8.99
Diluted (per share)	$ 3.56	$ 2.56	$ 8.26	$ 8.78
Weighted average common shares and common share equivalents outstanding
Basic (shares)	369.0	373.2	371.4	372.3
Diluted (shares)	376.1	382.3	379.1	381.3