Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		12 Months Ended
		Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Numerator:
Net income		$ 4,442	$ 1,482	$ 2,239
Net (income) loss attributable to noncontrolling interests		1	(6)	(82)
Net income available to Arch		4,443	1,476	2,157
Preferred share dividends		(40)	(40)	(48)
Loss on redemption of preferred shares		0	0	(15)
Net income available to Arch common shareholders		$ 4,403	$ 1,436	$ 2,094
Denominator:
Weighted average common shares outstanding		368.7	368.6	391.7
Effect of dilutive common share equivalents:
Nonvested restricted shares		2.5	2.1	2.0
Stock options	[1]	7.6	6.9	6.6
Weighted average common shares and common share equivalents outstanding — diluted		378.8	377.6	400.3
Earnings per common share:
Basic (per share)		$ 11.94	$ 3.90	$ 5.35
Diluted (per share)		$ 11.62	$ 3.80	$ 5.23
Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per common share (shares)		0.5	0.8	2.4

[1] Certain stock options were not included in the computation of diluted earnings per share where the exercise price of the stock options exceeded the average market price and would have been anti-dilutive or where, when applying the treasury stock method to in-the-money options, the sum of the proceeds, including unrecognized compensation, exceeded the average market price and would have been anti-dilutive. For 2023, 2022 and 2021, the number of stock options excluded were 0.5 million, 0.8 million and 2.4 million, respectively.