DEBT - Short-Term Borrowings (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Short-term Debt [Line Items]
Commercial paper	$ 17,126	$ 13,238
Other borrowings	25,316	19,108
Total short-term borrowings	42,442	32,346
Collateralized short-term advances from Federal Home Loan Bank	15,500	9,500
Bank
Short-term Debt [Line Items]
Commercial paper	12,895	13,238
Broker-dealer and other
Short-term Debt [Line Items]
Commercial paper	$ 4,231	$ 0