BUSINESS ACQUISITIONS - Schedule of Measurement Period Adjustments (Details) - Caliber - USD ($) $ in Millions				3 Months Ended	12 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Aug. 23, 2021	Dec. 31, 2021	Dec. 31, 2021
Business Acquisition [Line Items]
Total Consideration	$ 1,318.5	$ 1,318.5			$ 1,318.5
Assets
Mortgage servicing rights, at fair value	1,507.5	1,507.5		$ 1,507.5	1,507.5
Residential mortgage loans, held-for-sale, at fair value	7,685.7	7,685.7		7,685.7	7,685.7
Residential mortgage loans subject to repurchase	666.8	666.8		666.8	666.8
Cash and cash equivalents	472.7	472.7		472.7	472.7
Restricted cash	30.6	30.6		30.6	30.6
Servicer advance receivable	108.3	108.3		108.3	108.3
Intangible assets	41.0	41.0		41.0	41.0
Other assets	609.7	605.4		609.7	609.7
Other assets				4.3
Total Assets Acquired	11,122.3	11,118.0		11,122.3	11,122.3
Subsequent Adjustments to Fair Value, Total Assets Acquired				4.3
Liabilities
Secured financing agreements	7,090.6	7,090.6		7,090.6	7,090.6
Secured notes and bonds payable	1,121.8	1,121.8		1,121.8	1,121.8
Residential mortgage loans repurchase liability	666.8	666.8		666.8	666.8
Accrued expenses and other liabilities	918.6	917.0		918.6	918.6
Accrued expenses and other liabilities				1.6
Total Liabilities Assumed	9,797.8	9,796.2		9,797.8	9,797.8
Subsequent Adjustments to Fair Value, Total Liabilities Assumed				1.6
Net Assets	1,324.5	1,321.8		1,324.5	$ 1,324.5
Subsequent Adjustments to Fair Value, Net Assets				2.7
Bargain purchase gain	$ (6.0)	$ (3.3)	$ (3.3)	(6.0)
Subsequent Adjustment to Fair Value, Bargain purchase gain				$ (2.7)