FINANCIAL INSTRUMENTS - Fair Value of Derivatives (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Assets
Assets	$ 3,257	$ 3,364
Gross accrued interest recognized in statement of financial position	273	469
Gross derivatives recognized in statement of financial position	3,530	3,833
Netting adjustments offset in statement of financial position	(2,044)	(1,457)
Cash collateral offset in statement of financial position	(955)	(1,529)
Amounts offset in statement of financial position	(2,999)	(2,986)
Net derivatives	530	847
Securities held as collateral not offset in statement of financial position	(102)	(405)
Net amount	429	441
Liabilities
Amount	3,334	2,361
Gross accrued interest recognized in statement of financial position	(12)	(38)
Gross derivatives recognized in statement of financial position	3,322	2,323
Netting adjustments offset in statement of financial position	(2,043)	(1,456)
Cash collateral offset in statement of financial position	(763)	(578)
Amounts offset in statement of financial position	(2,807)	(2,034)
Net derivatives	515	289
Securities held as collateral not offset in statement of financial position	0	0
Net amount	515	289
Cumulative adjustment for non-performance risk	(1)	(1)
Excess cash collateral received	218	10
Excess cash collateral posted	425	255
Excess securities collateral received	7	16
Derivatives accounted for as hedges
Assets
Assets	1,632	2,021
Liabilities
Amount	360	218
Derivatives accounted for as hedges | Interest rate contracts
Assets
Assets	1,452	1,862
Liabilities
Amount	267	148
Derivatives accounted for as hedges | Currency exchange contracts
Assets
Assets	181	160
Liabilities
Amount	93	70
Derivatives not accounted for as hedges
Assets
Assets	1,625	1,343
Liabilities
Amount	2,975	2,143
Derivatives not accounted for as hedges | Interest rate contracts
Assets
Assets	37	93
Liabilities
Amount	2	8
Derivatives not accounted for as hedges | Currency exchange contracts
Assets
Assets	1,514	1,111
Liabilities
Amount	2,864	2,043
Derivatives not accounted for as hedges | Other contracts
Assets
Assets	74	139
Liabilities
Amount	$ 108	$ 91