Net Income (Loss) Per Share Attributable to Compass, Inc. - Schedule of Computation of Diluted Net Income (Loss) Per Share Attributable to Common Stockholders (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	29,331,581	41,986,096	99,630,257	72,622,712
Outstanding stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	9,434,758	27,803,123	31,063,765	36,118,246
Outstanding RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	19,896,823	14,006,659	55,133,929	35,966,151
Shares subject to the Employee Stock Purchase Plan
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	0	173,744	274,665	361,903
Unvested early exercised stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	0	2,570	0	2,570
Unvested common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	0	0	50,704	173,842
Incremental common stock to be issued in connection with the Share Consideration
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	0	0	13,107,194	0