Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Comprehensive Income
Net income	$ 4,442	$ 1,482	$ 2,239
Unrealized appreciation (decline) in value of available-for-sale investments:
Unrealized holding gains (losses) arising during year	547	(1,772)	(386)
Reclassification of net realized (gains) losses, included in net income	400	247	(117)
Foreign currency translation adjustments	23	(56)	(65)
Comprehensive income (loss)	5,412	(99)	1,671
Net (income) loss attributable to noncontrolling interests	1	(6)	(82)
Other comprehensive (income) loss attributable to noncontrolling interests	0	0	14
Comprehensive income available to Arch (loss)	$ 5,413	$ (105)	$ 1,603