CHANGES IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (AOCI) - Reclassification out of AOCI (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Realized (gains) losses on sales of investments	[1]									$ (778)	$ (948)	$ (682)
Income from continuing operations before income taxes		$ (5,099)	$ (6,003)	$ (5,678)	$ (5,981)	$ (5,100)	$ (5,620)	$ (5,770)	$ (4,987)
Tax effect		23,864	1,866	1,795	1,863	1,509	1,733	1,723	1,479	29,388	6,444	7,440
Income from continuing operations		$ 18,765	$ (4,137)	$ (3,883)	$ (4,118)	$ (3,591)	$ (3,887)	$ (4,047)	$ (3,508)	6,627	(15,033)	(17,386)
Reclassification from AOCI, after-tax										(213)	(119)	92
Realized gains (losses) on investment securities
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Reclassification from AOCI, after-tax										(454)	(422)	(269)
Debt valuation adjustment (DVA)
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Reclassification from AOCI, after-tax										(4)	(2)	0
Cash flow hedges
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Reclassification from AOCI, after-tax										86	145	209
Prior service cost (benefit)
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Reclassification from AOCI, before tax										(42)	(40)	(40)
Net actuarial loss
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Reclassification from AOCI, before tax										271	272	276
Curtailment/settlement impact
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Reclassification from AOCI, before tax										17	18	57
Benefit plans
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Reclassification from AOCI, before tax										246	250	293
Tax effect										(87)	(90)	(107)
Reclassification from AOCI, after-tax										159	160	186
Foreign currency translation adjustment
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Reclassification from AOCI, after-tax										0	0	(34)
Accumulated other comprehensive income (loss)
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Reclassification from AOCI, before tax										(340)	(180)	155
Tax effect										127	61	(63)
Reclassification from AOCI, after-tax										(213)	(119)	92
(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										(778)	(948)	(682)
OTTI gross impairment losses										63	288	265
Income from continuing operations before income taxes										(715)	(660)	(417)
Tax effect										261	238	148
Income from continuing operations										(454)	(422)	(269)
(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										(7)	(3)	0
Income from continuing operations before income taxes										(7)	(3)	0
Tax effect										3	1	0
Income from continuing operations										(4)	(2)	0
(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										136	233	332
Tax effect										(50)	(88)	(123)
Income from continuing operations										86	145	209
(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										126	140	186
(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										10	93	146
(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	0	(53)
Tax effect										0	0	19
Income from continuing operations										$ 0	$ 0	$ (34)

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