PLEDGED ASSETS, COLLATERAL, GUARANTEES AND COMMITMENTS - Lease Commitments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Lessee, Lease, Description [Line Items]
Operating lease, right-of-use asset	$ 3,100
Operating lease liability	3,340	$ 3,300
Sublease income	56
Operating lease expense	1,084
Operating cash outflows related to operating leases	$ 942
Operating lease, weighted average discount rate	3.60%
Future Lease Payments After Adoption
2020	$ 801
2021	695
2022	572
2023	425
2024	314
Thereafter	935
Lessee, Operating Lease, Liability, Payments, Due	3,742
Less imputed interest (based on weighted-average discount rate of 3.6%)	(402)
Lease liability	$ 3,340	3,300
Future Minimum Annual Rentals Before Adoption
2019		925
2020		748
2021		657
2022		525
2023		394
Thereafter		1,890
Total lease commitments		5,139
Operating lease expense		$ 1,000	$ 1,100
Weighted Average
Lessee, Lease, Description [Line Items]
Operating lease term	6 years