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, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	25,487,217	29,331,581	5,942,416	99,630,257
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)	3,488,591	9,434,758	2,351,675	31,063,765
Outstanding RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	21,763,509	19,896,823	3,590,741	55,133,929
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)	235,117	0	0	274,665
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	0	50,704
Incremental common stock to be issued in connection with the CIRE 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	0	13,107,194