CHANGES IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (AOCI) - Reclassification out of AOCI (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Realized (gains) losses on sales of investments	[1]									$ (421)	$ (778)	$ (949)
Income from continuing operations before income taxes		$ (5,306)	$ (6,104)	$ (5,945)	$ (6,090)	$ (5,099)	$ (6,003)	$ (5,678)	$ (5,981)
Tax effect		1,001	1,471	1,444	1,441	23,864	1,866	1,795	1,863	5,357	29,388	6,444
Income from continuing operations		$ (4,305)	$ (4,633)	$ (4,501)	$ (4,649)	$ 18,765	$ (4,137)	$ (3,883)	$ (4,118)	(18,088)	6,627	(15,033)
Realized gains (losses) on investment securities
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Reclassification from AOCI, after-tax										(223)	(454)	(423)
Debt valuation adjustment (DVA)
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Reclassification from AOCI, after-tax										32	(4)	(2)
Cash flow hedges
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Reclassification from AOCI, after-tax										105	86	145
Prior service cost (benefit)
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Reclassification from AOCI, before tax										(34)	(42)	(40)
Net actuarial loss
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Reclassification from AOCI, before tax										248	271	272
Curtailment/settlement impact
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Reclassification from AOCI, before tax										6	17	18
Benefit plans
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Reclassification from AOCI, before tax										220	246	250
Tax effect										(54)	(87)	(90)
Reclassification from AOCI, after-tax										166	159	160
Foreign currency translation adjustment
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Reclassification from AOCI, after-tax										245	0	0
Accumulated other comprehensive income (loss)
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Reclassification from AOCI, before tax										137	(340)	(181)
Tax effect										188	127	61
Reclassification from AOCI, after-tax										325	(213)	(120)
(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										(421)	(778)	(949)
Gross impairment losses										125	63	288
Income from continuing operations before income taxes										(296)	(715)	(661)
Tax effect										73	261	238
Income from continuing operations										(223)	(454)	(423)
(Gain) loss reclassified from AOCI | Debt valuation adjustment (DVA)
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Realized (gains) losses on sales of investments										41	(7)	(3)
Income from continuing operations before income taxes										41	(7)	(3)
Tax effect										(9)	3	1
Income from continuing operations										32	(4)	(2)
(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										138	136	233
Tax effect										(33)	(50)	(88)
Income from continuing operations										105	86	145
(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										131	126	140
(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	10	93
(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										34	0	0
Tax effect										211	0	0
Income from continuing operations										$ 245	$ 0	$ 0

[1] Certain prior-period revenue and expense lines and totals were reclassified to conform to the current period’s presentation. See Notes 1 and 3 to the Consolidated Financial Statements.