Unaudited Consolidated Statements of 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	$ 3,248	$ 2,471	$ 9,096	$ 6,918
Net investment income	269	129	710	315
Net realized gains (losses)	(248)	(184)	(354)	(743)
Other underwriting income	5	3	21	12
Equity in net income (loss) of investment funds accounted for using the equity method	59	(19)	176	75
Other income (loss)	(4)	(14)	10	(35)
Total revenues	3,329	2,386	9,659	6,542
Expenses
Losses and loss adjustment expenses	1,647	1,683	4,609	3,787
Acquisition expenses	575	448	1,669	1,239
Other operating expenses	310	275	942	842
Corporate expenses	20	18	71	78
Amortization of intangible assets	24	26	71	80
Interest expense	34	33	99	99
Net foreign exchange (gains) losses	(22)	(91)	1	(183)
Total expenses	2,588	2,392	7,462	5,942
Income (loss) before income taxes and income (loss) from operating affiliates	741	(6)	2,197	600
Income tax (expense) benefit	(72)	15	(203)	(19)
Income (loss) from operating affiliates	54	9	115	39
Net income (loss)	723	18	2,109	620
Net (income) loss attributable to noncontrolling interests	0	(1)	0	(3)
Net income (loss) available to Arch	723	17	2,109	617
Preferred dividends	(10)	(10)	(30)	(30)
Net income (loss) available to Arch common shareholders	$ 713	$ 7	$ 2,079	$ 587
Net income per common share and common share equivalent
Basic (per share)	$ 1.93	$ 0.02	$ 5.64	$ 1.59
Diluted (per share)	$ 1.88	$ 0.02	$ 5.50	$ 1.55
Weighted average common shares and common share equivalents outstanding
Basic (shares)	369.2	365.2	368.4	369.5
Diluted (shares)	379.4	373.7	378.3	378.4