BASIS OF PRESENTATION AND ACCOUNTING CHANGES - Accounting Changes (Details) - USD ($) $ in Millions		3 Months Ended
	Jan. 01, 2020	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle
Allowance for credit losses		$ 20,841	$ 12,329	$ 12,783	$ 12,315
Decrease in retained earnings		(163,438)		(165,369)
Build to allowance for credit losses		$ 4,112	$ 67
Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle
Allowance for credit losses				$ 4,201
Accounting Standards Update 2016-13
New Accounting Pronouncements or Change in Accounting Principle
Pretax percentage increase allowance for credit losses	29.00%
Loss coverage period	23 months
Release of reserves	$ 800
Accounting Standards Update 2016-13 | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle
Allowance for credit losses	4,100
Decrease in retained earnings	3,100
Increase in deferred tax assets	1,000
Build to allowance for credit losses	$ 4,900
Accounting Guidance Prior to Adoption of Accounting Standards Update 2016-13
New Accounting Pronouncements or Change in Accounting Principle
Loss coverage period	14 months