Unaudited Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Comprehensive Income
Net income (loss)	$ 1,120	$ 717
Unrealized appreciation (decline) in value of available-for-sale investments:
Unrealized holding gains (losses) arising during period	(141)	245
Reclassification of net realized (gains) losses, included in net income (loss)	29	99
Foreign currency translation adjustments	(33)	5
Comprehensive income (loss)	975	1,066
Net (income) loss attributable to noncontrolling interests	0	(2)
Comprehensive income (loss) available to Arch	$ 975	$ 1,064