Compensation - Narrative (Detail)			3 Months Ended		6 Months Ended	12 Months Ended
	Jul. 01, 2023 USD ($) shares	Jun. 30, 2023 USD ($) shares	Mar. 31, 2024 USD ($) shares	Mar. 31, 2023 USD ($) shares	Jun. 30, 2023 USD ($)	Dec. 31, 2023 USD ($) 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)			469,400,000
Number of share-equivalent limited partnership units exchangeable into shares (in shares)			0			0
Number of common stock settled per restricted stock unit (in shares)			1
Estimated fair value of restricted stock units | $			$ 5,300,000
Aggregate estimated fair value of limited partnership units and restricted stock units | $						$ 7,400,000
Aggregate estimated fair value of deferred compensation awards | $			$ 0		$ 600,000
Number of shares released the restrictions (in shares)			0	0
Shares withheld to satisfy tax liabilities (in shares)			1,400,000
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 | $			$ 24,514,000
Unrecognized compensation expense related to unvested | $			$ 168,900,000
Unrecognized compensation expense related to unvested recognized period			5 years 8 months 4 days
Weighted- Average Remaining Contractual Term (Years)			5 years 8 months 4 days			5 years 11 months 15 days
Limited partnership units outstanding (in shares)			63,288,000			64,942,000
Restricted Stock Units (RSUs) | Eligible
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Limited partnership units outstanding (in shares)			25,400,000
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 | $			$ 0
Unrecognized compensation expense related to unvested | $			$ 28,300,000
Weighted- Average Remaining Contractual Term (Years)			1 year 18 days			2 years 6 months 18 days
Limited partnership units outstanding (in shares)			21,472,000			27,953,000
Share-based payment arrangement, expense | $			$ 35,500,000
Accelerated vesting of restricted stock (in shares)			4,300,000
Accelerated vesting expense | $			$ 25,400,000
Shares withheld to satisfy tax liabilities (in shares)			1,400,000
Restricted Shares | Eligible
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Limited partnership units outstanding (in shares)			1,300,000
Restricted Stock Units, Tax Account
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock redeemed during period (in shares)	16,300,000
Stock issued during period | $		$ 49,200,000
Granted | $	$ 74,000,000	$ 123,100,000
Unrecognized compensation expense related to unvested | $			$ 86,000,000
Vested | $			$ 3,500,000
Weighted- Average Remaining Contractual Term (Years)			8 years 7 months 9 days
Share-based payment arrangement, expense | $			$ 6,000,000
Restricted BGC Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Limited partnership units outstanding (in shares)			0			100,000
Restricted Newmark Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of outstanding restricted shares held (in shares)			0			0
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)	9,900,000	10,600,000
Minimum | Restricted Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares saleable period			5 years
Maximum | Restricted Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares saleable period			10 years
LPUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding (in shares)			0			0
Common stock exchangeable basis			1
Limited partnership interests exchange ratio			0.9255
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
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares released the restrictions (in shares)			0	0
Newmark | LPUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Limited partnership units outstanding (in shares)			8,655,000			8,779,000
Newmark | LPUs | REUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
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
Notional value with post-termination pay-out amount | $			$ 700,000
Aggregate estimated fair value of limited partnership units | $			$ 300,000
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)			200,000	0
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
Shares, forfeited (in shares)			636,167	49,201
Shares withheld to satisfy tax liabilities (in shares)			11,000,000	0
Stock issued to employees (in shares)			2,300,000	0
Class A Common Stock | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Value of shares withheld | $			$ 11,800,000	$ 6,200,000
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