GUARANTEES, LEASES AND COMMITMENTS - Leases (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Operating lease term	9 years
Operating lease ROU asset	$ 4,100
Operating lease, liability	4,112
Sublease income	19
Operating lease expense	270
Operating cash outflows related to operating leases	234
Operating Lease Liabilities, Payments Due [Abstract]
2019 (excluding the three months ended March 31, 2019)	704
2020	755
2021	638
2022	514
2023	405
Thereafter	1,794
Total future lease payments	4,810
Less imputed interest (based on weighted-average discount rate of 3.5%)	(698)
Lease liability	$ 4,112
Operating lease, weighted average discount rate	3.50%