BASIS OF PRESENTATION, UPDATED ACCOUNTING POLICIES AND ACCOUNTING CHANGES - Accounting Changes (Details) - USD ($) $ in Millions		3 Months Ended			6 Months Ended
	Jan. 01, 2020	Sep. 30, 2020	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle
Allowance for credit losses			$ 26,420	$ 12,466	$ 26,420	$ 12,466	$ 20,841	$ 12,783	$ 12,329	$ 12,315
Pretax percentage increase allowance for credit losses	29.00%
Decrease in retained earnings			(163,431)		(163,431)			(165,369)
Build to allowance for credit losses			4,856	53	8,968	120
Reduction in collection costs from credit recoveries			(322)	(391)	(693)	(788)
Increase in operating expenses			10,415	$ 10,500	$ 21,009	$ 21,084
Accounting Standards Update [Extensible List]					us-gaap:AccountingStandardsUpdate201613Member
Revision of Prior Period, Change in Accounting Principle, Adjustment
New Accounting Pronouncements or Change in Accounting Principle
Allowance for credit losses			$ (426)		$ (426)
Revision of Prior Period, Reclassification, Adjustment | Forecast
New Accounting Pronouncements or Change in Accounting Principle
Reduction in collection costs from credit recoveries		$ 50
Increase in operating expenses		$ 50
Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle
Allowance for credit losses	$ 4,100						$ 0	$ 4,201		$ 0
Decrease in retained earnings	3,100
Increase in deferred tax assets	1,000
Build to allowance for credit losses	4,900
Release of reserves	$ 800
Accounting Standards Update 2016-13
New Accounting Pronouncements or Change in Accounting Principle
Loss coverage period	23 months
Accounting Guidance Prior to Adoption of Accounting Standards Update 2016-13
New Accounting Pronouncements or Change in Accounting Principle
Loss coverage period	14 months