DERIVATIVES ACTIVITIES - Cash Flow Hedges (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pretax change in accumulated other comprehensive income (loss)
Amount of gain (loss) recognized in AOCI on derivative	$ 729	$ (356)	$ (173)
Other revenue	1,448	1,661	1,437
Net interest revenue	47,347	46,562	45,061
Cash flow hedges expected to be reclassified within 12 months	$ 84
Maximum length of time hedged in cash flow hedge	10 years
Interest rate contracts
Pretax change in accumulated other comprehensive income (loss)
Amount of gain (loss) recognized in AOCI on derivative	$ 746	(361)	(165)
Foreign exchange contracts
Pretax change in accumulated other comprehensive income (loss)
Amount of gain (loss) recognized in AOCI on derivative	(17)	5	(8)
Cash flow hedges
Pretax change in accumulated other comprehensive income (loss)
Net interest revenue	1,120	(38)	(37)
Amount of gain (loss) reclassified from AOCI to earnings \| Cash flow hedges
Pretax change in accumulated other comprehensive income (loss)
Other revenue	(7)	(17)	(136)
Net interest revenue	(384)	(301)
Amount of gain (loss) reclassified from AOCI to earnings \| Cash flow hedges \| Interest rate contracts
Pretax change in accumulated other comprehensive income (loss)
Other revenue	0	0	(126)
Net interest revenue	(384)	(301)
Amount of gain (loss) reclassified from AOCI to earnings \| Cash flow hedges \| Foreign exchange contracts
Pretax change in accumulated other comprehensive income (loss)
Other revenue	(7)	(17)	$ (10)
Net interest revenue	$ 0	$ 0

The estimated net amount of existing gains or losses on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months.

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The net amount of operating interest income (expense).

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Maximum length of time over which the entity is hedging its exposure to the variability in future cash flows for forecasted transactions, excluding those forecasted transactions related to the payment of variable interest on existing financial instruments, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount, before tax and after reclassification, of gain (loss) from derivative instrument designated and qualifying cash flow hedge included in assessment of hedge effectiveness, attributable to parent.

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- Definition

Amount of income (expense) related to nonoperating activities, classified as other.

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