DESCRIPTION OF BUSINESS, BASIS OF PRESENTATION AND ACCOUNTING POLICIES (Recently Adopted Accounting Standards) (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019		Sep. 30, 2020		Jun. 30, 2020	Jan. 01, 2020	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201602Member	us-gaap:AccountingStandardsUpdate201613Member
Financing receivable, allowance for credit loss			$ 3,646,189	[1]	$ 7,399,598	[1]	$ 7,112,738		$ 3,735,860	$ 3,783,833	$ 3,897,130
Stockholders' equity			24,398,830		20,804,971		$ 20,226,777		$ 24,669,277	$ 24,504,819	$ 23,847,232
Deferred tax liabilities, net			(1,000,000)		$ (69,200)
Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing receivable, allowance for credit loss			2,535,882
Stockholders' equity			(1,800,000)
ASU 2016-13
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing receivable, allowance for credit loss								$ 2,500,000
Deferred tax liabilities, net								$ 700,000
ASU 2016-13 | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' equity			$ (1,785,464)

[1] The Company has interests in certain Trusts that are considered VIEs for accounting purposes. At September 30, 2020 and December 31, 2019, LHFI included $22.7 billion and $26.5 billion, Operating leases assets, net included $16.2 billion and $16.5 billion, restricted cash included $1.8 billion and $1.6 billion, other assets included $870.2 million and $625.4 million, Borrowings and other debt obligations included $31.3 billion and $34.2 billion, and Other liabilities included $118.0 million and $188.1 million of assets or liabilities that were included within VIEs, respectively. See Note 7 to these Condensed Consolidated Financial Statements for additional information.