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CHANGES IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (AOCI) - Reclassification out of AOCI (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Realized (gains) losses on sales of investments									$ (1,474)	$ (421)	$ (778)
Income from continuing operations before income taxes	$ (5,702)	$ (6,022)	$ (6,165)	$ (6,012)	$ (5,306)	$ (6,104)	$ (5,945)	$ (6,090)
Tax effect	703	1,079	1,373	1,275	1,001	1,471	1,444	1,441	4,430	5,357	29,388
Income from continuing operations	$ (4,999)	$ (4,943)	$ (4,792)	$ (4,737)	$ (4,305)	$ (4,633)	$ (4,501)	$ (4,649)	(19,471)	(18,088)	6,627
Realized gains (losses) on investment securities
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Reclassification from AOCI, after-tax									(1,080)	(223)	(454)
Debt valuation adjustment (DVA)
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Reclassification from AOCI, after-tax									15	32	(4)
Cash flow hedges
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Reclassification from AOCI, after-tax									302	105	86
Prior service cost (benefit)
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Reclassification from AOCI, before tax									(12)	(34)	(42)
Net actuarial loss
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Reclassification from AOCI, before tax									286	248	271
Curtailment/settlement impact
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Reclassification from AOCI, before tax									1	6	17
Benefit plans
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Reclassification from AOCI, before tax									275	220	246
Tax effect									(69)	(54)	(87)
Reclassification from AOCI, after-tax									206	166	159
Foreign currency translation adjustment
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Reclassification from AOCI, after-tax									326	245	0
Accumulated other comprehensive income (loss)
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Reclassification from AOCI, before tax									(765)	317	(340)
Tax effect									534	8	127
Reclassification from AOCI, after-tax									(231)	325	(213)
(Gain) loss reclassified from AOCI \| Realized gains (losses) on investment securities
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Realized (gains) losses on sales of investments									(1,474)	(421)	(778)
Gross impairment losses									23	125	63
Income from continuing operations before income taxes									(1,451)	(296)	(715)
Tax effect									371	73	261
Income from continuing operations									(1,080)	(223)	(454)
(Gain) loss reclassified from AOCI \| Debt valuation adjustment (DVA)
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Income from continuing operations before income taxes									20	41	(7)
Tax effect									(5)	(9)	3
Income from continuing operations									15	32	(4)
(Gain) loss reclassified from AOCI \| Cash flow hedges
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Income from continuing operations before income taxes									391	318	136
Tax effect									(89)	(213)	(50)
Income from continuing operations									302	105	86
(Gain) loss reclassified from AOCI \| Cash flow hedges \| Interest rate
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Income from continuing operations before income taxes									384	301	126
(Gain) loss reclassified from AOCI \| Cash flow hedges \| Foreign exchange contracts
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Income from continuing operations before income taxes									7	17	10
(Gain) loss reclassified from AOCI \| Foreign currency translation adjustment
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Income from continuing operations before income taxes									0	34	0
Tax effect									326	211	0
Income from continuing operations									$ 326	$ 245	$ 0