Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Comprehensive Income
Net income	$ 4,312	$ 4,442	$ 1,482
Unrealized appreciation (decline) in value of available-for-sale investments:
Unrealized holding gains (losses) arising during year	(23)	547	(1,772)
Reclassification of net realized (gains) losses, included in net income	81	400	247
Foreign currency translation adjustments	(102)	23	(56)
Comprehensive income (loss)	4,268	5,412	(99)
Net (income) loss attributable to noncontrolling interests	0	1	(6)
Comprehensive income available to Arch (loss)	$ 4,268	$ 5,413	$ (105)