DERIVATIVES - Cash Flow Hedges (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Pretax change in accumulated other comprehensive income (loss)
Amount of gain (loss) recognized in AOCI on derivative	$ 3	$ (52)	$ (413)	$ 2,723
Net pretax change in cash flow hedges included within AOCI	(265)	(307)	(1,219)	2,267
Cash flow hedge gain expected to be reclassified from AOCI within 12 months			$ 1,000
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	19	(52)	$ (397)	2,739
Foreign exchange contracts
Pretax change in accumulated other comprehensive income (loss)
Amount of gain (loss) recognized in AOCI on derivative	(16)	0	(16)	(16)
Other revenue
Pretax change in accumulated other comprehensive income (loss)
Amount of gain (loss) reclassified from AOCI to earnings	(1)	(1)	(3)	(3)
Other revenue | Interest rate contracts
Pretax change in accumulated other comprehensive income (loss)
Amount of gain (loss) reclassified from AOCI to earnings	0	0	0	0
Other revenue | Foreign exchange contracts
Pretax change in accumulated other comprehensive income (loss)
Amount of gain (loss) reclassified from AOCI to earnings	(1)	(1)	(3)	(3)
Net interest revenue
Pretax change in accumulated other comprehensive income (loss)
Amount of gain (loss) reclassified from AOCI to earnings	269	256	809	459
Net interest revenue | Interest rate contracts
Pretax change in accumulated other comprehensive income (loss)
Amount of gain (loss) reclassified from AOCI to earnings	269	256	809	459
Net interest revenue | Foreign exchange contracts
Pretax change in accumulated other comprehensive income (loss)
Amount of gain (loss) reclassified from AOCI to earnings	$ 0	$ 0	$ 0	$ 0