Unaudited Consolidated Statements of Income - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Revenues
Net premiums earned	$ 3,565	$ 2,965	$ 6,987	$ 5,848
Net investment income	364	242	691	441
Net realized gains (losses)	122	(123)	189	(106)
Other underwriting income	3	6	15	16
Equity in net income (loss) of investment funds accounted for using the equity method	167	69	266	117
Other income (loss)	8	3	22	14
Total revenues	4,229	3,162	8,170	6,330
Expenses
Losses and loss adjustment expenses	1,827	1,491	3,555	2,962
Acquisition expenses	633	561	1,240	1,094
Other operating expenses	346	313	709	632
Corporate expenses	41	21	94	51
Amortization of intangible assets	27	24	48	47
Interest expense	35	33	69	65
Net foreign exchange (gains) losses	(1)	5	(32)	23
Total expenses	2,908	2,448	5,683	4,874
Income (loss) before income taxes and income (loss) from operating affiliates	1,321	714	2,487	1,456
Income tax (expense) benefit	(97)	(67)	(198)	(131)
Income (loss) from operating affiliates	45	22	100	61
Net income (loss)	1,269	669	2,389	1,386
Net (income) loss attributable to noncontrolling interests	0	2	0	0
Net income (loss) available to Arch	1,269	671	2,389	1,386
Preferred dividends	(10)	(10)	(20)	(20)
Net income (loss) available to Arch common shareholders	$ 1,259	$ 661	$ 2,369	$ 1,366
Net income per common share and common share equivalent
Basic (per share)	$ 3.38	$ 1.79	$ 6.37	$ 3.71
Diluted (per share)	$ 3.30	$ 1.75	$ 6.22	$ 3.62
Weighted average common shares and common share equivalents outstanding
Basic (shares)	372.7	368.7	371.8	368.0
Diluted (shares)	381.6	378.4	380.9	377.8