Limited Partnership Interests in BGC Holdings and Newmark Holdings (Detail) shares in Millions				3 Months Ended	12 Months Ended
	Nov. 30, 2018 shares	Nov. 23, 2018 shares	Jun. 05, 2015 shares	Dec. 31, 2021 installment	Dec. 31, 2021 partnership installment
Noncontrolling Interest [Abstract]
Number of operating partnerships | partnership					2
Limited partnership interest, conversion ratio				1	1
Number of installment | installment				4	4
Quarterly Percentage to preferred units				0.006875	0.006875
Percentage to preferred units					2.75%
CF Group Management, Inc.
Noncontrolling Interest [Abstract]
Number of shares, right to exchange from Class A to Class B common stock (in shares) | shares	23.6	0.7	34.6
Newmark Holdings
Noncontrolling Interest [Abstract]
Calculation of contribution ratio, denominator				2.2	2.2
Limited partnership interest, conversion ratio				1	1
BGC Holdings LPUs
Noncontrolling Interest [Abstract]
Limited partnership interest, conversion ratio				1	1