SECURITIES - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Investments, Debt and Equity Securities [Abstract]
Residential Investment securities sold, carrying value	$ 9,100.0	$ 2,900.0	$ 19,500.0	$ 3,400.0
Residential Investment securities sold, net realized gain (loss)	$ (34.3)	$ (63.1)	$ (126.8)	$ (50.0)