Unaudited Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Comprehensive Income
Net income (loss)	$ 723	$ 18	$ 2,109	$ 620
Unrealized appreciation (decline) in value of available-for-sale investments:
Unrealized holding gains (losses) arising during period	(190)	(610)	(118)	(1,892)
Reclassification of net realized (gains) losses, included in net income (loss)	96	46	344	206
Foreign currency translation adjustments	(40)	(70)	(33)	(141)
Comprehensive income (loss)	589	(616)	2,302	(1,207)
Net (income) loss attributable to noncontrolling interests	0	(1)	0	(3)
Comprehensive income (loss) available to Arch	$ 589	$ (617)	$ 2,302	$ (1,210)