Compensation - Narrative (Detail)			3 Months Ended		9 Months Ended		12 Months Ended
	Jul. 01, 2023 USD ($) shares	Jun. 30, 2023 USD ($) shares	Sep. 30, 2023 USD ($) shares	Sep. 30, 2022 USD ($) shares	Sep. 30, 2023 USD ($) shares	Sep. 30, 2022 USD ($) shares	Dec. 31, 2022 USD ($) shares	Nov. 22, 2021 shares	Nov. 21, 2021 shares	Jul. 01, 2021 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate number of shares grant of future awards (in shares)			487,300,000		487,300,000
Issuance of restricted stock upon redemption of limited partnership interests (in shares)			38,610,233	0	38,610,233	0
Restricted stock issued during period | $			$ 0		$ 0
Number of share-equivalent limited partnership units exchangeable into shares (in shares)			0		0		1,200,000
Number of common stock settled per restricted stock unit (in shares)					1
Estimated fair value of restricted stock units | $					$ 4,400,000
Aggregate estimated fair value of limited partnership units and restricted stock units | $							$ 5,900,000
Aggregate estimated fair value of deferred compensation awards | $					$ 0		$ 23,900,000
Number of shares released the restrictions (in shares)			0	100,000	2,300,000	200,000
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issuance of restricted stock upon redemption of limited partnership interests (in shares)	25,300,000	22,500,000
Granted | $					$ 243,885,000
Unrecognized compensation expense related to unvested | $			$ 150,400,000		$ 150,400,000
Unrecognized compensation expense related to unvested recognized period					6 years 4 months 13 days
Weighted- Average Remaining Contractual Term (Years)					6 years 4 months 13 days		2 years 5 months 1 day
Limited partnership units outstanding (in shares)			62,230,000		62,230,000		12,046,000
Restricted Stock Units (RSUs) | Eligible
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Limited partnership units outstanding (in shares)			28,000,000		28,000,000
Restricted Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issuance of restricted stock upon redemption of limited partnership interests (in shares)	38,600,000
Granted | $					$ 168,716,000
Unrecognized compensation expense related to unvested | $			$ 52,300,000		$ 52,300,000
Unrecognized compensation expense related to unvested recognized period					2 years 3 months 14 days
Weighted- Average Remaining Contractual Term (Years)					2 years 3 months 14 days
Limited partnership units outstanding (in shares)			32,369,000		32,369,000		0
Share-based payment arrangement, expense | $			$ 17,400,000		$ 17,400,000
Restricted Shares | Eligible
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Limited partnership units outstanding (in shares)			5,800,000		5,800,000
Restricted Stock Units, Tax Account
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock issued during period | $		$ 49,200,000
Granted | $	$ 74,000,000	$ 123,100,000
Unrecognized compensation expense related to unvested | $			$ 111,700,000		$ 111,700,000
Vested | $			10,600,000
Weighted- Average Remaining Contractual Term (Years)					8 years 6 months 3 days
Share-based payment arrangement, expense | $			$ 13,100,000		$ 13,100,000
Restricted BGC Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Limited partnership units outstanding (in shares)			100,000		100,000		2,300,000
Restricted Newmark Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares released the restrictions (in shares)			0	0	1,100,000	100,000
Number of outstanding restricted shares held (in shares)			0		0		1,100,000
Non-exchangeable LPUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock redeemed during period (in shares)	54,000,000	16,900,000
Non-exchangeable FPUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock redeemed during period (in shares)		5,600,000
Non-exchangeable PSU
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock redeemed during period (in shares)	16,300,000	10,600,000
Minimum | Restricted Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted- Average Remaining Contractual Term (Years)					5 years
Restricted shares saleable period					5 years
Maximum | Restricted Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted- Average Remaining Contractual Term (Years)					10 years
Restricted shares saleable period					10 years
LPUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock exchangeable basis					1
Limited partnership interests exchange ratio					0.9243
Limited partnership units outstanding (in shares)			0		0		110,348,000
LPUs | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares, restriction period					2 years
LPUs | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares, restriction period					5 years
Newmark | LPUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Limited partnership units outstanding (in shares)			8,905,000		8,905,000		9,351,000
Newmark | LPUs | REUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding (in shares)			0		0
Notional value with post-termination pay-out amount | $							$ 700,000
Aggregate estimated fair value of limited partnership units | $							$ 300,000
BGC Holdings | LPUs | REUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding (in shares)			100,000		100,000		800,000
Notional value with post-termination pay-out amount | $			$ 600,000		$ 600,000		$ 8,600,000
Aggregate estimated fair value of limited partnership units | $			$ 200,000		$ 200,000		$ 3,900,000
Number of outstanding limited partnership units, unvested (in shares)							100,000
BGC or Newmark | Restricted Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, forfeited (in shares)			0	43,000	200,000	47,000
Class A Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of share-equivalent limited partnership units exchangeable into shares (in shares)			200,000		200,000		200,000
Shares, forfeited (in shares)			0	43,388	238,927	47,807
Class A Common Stock | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Value of shares withheld | $			$ 2,700,000	$ 200,000	$ 10,200,000	$ 6,400,000
Equity plan | Class A Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized to be delivered pursuant to awards granted (in shares)								500,000,000	400,000,000	600,000,000