SECURITIES - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Investments, Debt and Equity Securities [Abstract]
Residential Investment securities sold, carrying value	$ 11,100.0	$ 9,100.0	$ 30,700.0	$ 14,500.0
Residential Investment securities sold, net realized gains (losses)	$ 76.3	$ (322.4)	$ (50.6)	$ (372.5)