PREFERRED STOCK - Additional Information (Details) - USD ($) shares in Thousands, $ in Millions	3 Months Ended				12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Distribution of preferred dividends					$ 1,109
Preferred stock dividends declared					$ 1,109	$ 1,174	$ 1,213
Subsequent event
Class of Stock [Line Items]
Preferred stock dividends declared				$ 291
Preferred Stock
Class of Stock [Line Items]
Issuance of new preferred stock (in shares)					60
Issuance of new preferred stock					$ 1,500
Preferred Stock | Subsequent event | Series V
Class of Stock [Line Items]
Issuance of new preferred stock (in shares)				1,500
Issuance of new preferred stock				$ 1,500
Forecast
Class of Stock [Line Items]
Distribution of preferred dividends	$ 253	$ 328	$ 253