Consolidated Statements of Income - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Revenues
Net premiums earned	$ 15,100	$ 12,440	$ 9,679
Net investment income	1,495	1,023	496
Net realized gains (losses)	197	(165)	(663)
Other underwriting income	26	31	13
Equity in net income of investments accounted for using the equity method	580	278	115
Other income (loss)	42	27	(27)
Total revenues	17,440	13,634	9,613
Expenses
Losses and loss adjustment expenses	8,342	6,246	5,028
Acquisition expenses	2,651	2,312	1,740
Other operating expenses	1,472	1,301	1,128
Corporate expenses	200	102	95
Amortization of intangible assets	235	95	106
Interest expense	141	133	131
Net foreign exchange losses (gains)	(75)	60	(102)
Total expenses	12,966	10,249	8,126
Income before income taxes and income (loss) from operating affiliates	4,474	3,385	1,487
Income taxes:
Current tax expense (benefit)	397	288	201
Deferred tax expense (benefit)	(35)	(1,161)	(121)
Income tax expense (benefit)	362	(873)	80
Income (loss) from operating affiliates	200	184	75
Net income	4,312	4,442	1,482
Net (income) loss attributable to noncontrolling interests	0	1	(6)
Net income available to Arch	4,312	4,443	1,476
Preferred share dividends	(40)	(40)	(40)
Net income available to Arch common shareholders	$ 4,272	$ 4,403	$ 1,436
Net income per common share and common share equivalent
Basic (per share)	$ 11.47	$ 11.94	$ 3.90
Diluted (per share)	$ 11.19	$ 11.62	$ 3.80
Weighted average common shares and common share equivalents outstanding
Basic (shares)	372.5	368.7	368.6
Diluted (shares)	381.8	378.8	377.6