BASIS OF PRESENTATION, UPDATED ACCOUNTING POLICIES AND ACCOUNTING CHANGES - Accounting Changes (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
	Jan. 01, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses		$ 26,426	$ 12,530	$ 26,426	$ 12,530	$ 26,420	$ 12,783	$ 12,466	$ 12,315
Pretax percentage increase allowance for credit losses	29.00%
Decrease in retained earnings		(165,303)		(165,303)			(165,369)
Build to allowance for credit losses		42	132	9,010	252
Reduction in collection costs from credit recoveries		(448)	(368)	(1,141)	(1,156)
Increase in operating expenses		$ 10,964	$ 10,464	$ 31,973	$ 31,548
Accounting Standards Update [Extensible List]				us-gaap:AccountingStandardsUpdate201613Member
Change in Accounting Principle, Type [Extensible List]		us-gaap:ChangeInAccountingPrincipleOtherMember
Revision of Prior Period, Change in Accounting Principle, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses		$ (122)		$ (122)		(426)
Revision of Prior Period, Reclassification, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
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 [Line Items]
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 [Line Items]
Loss coverage period	23 months
Accounting Guidance Prior to Adoption of Accounting Standards Update 2016-13
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loss coverage period	14 months