CHANGES IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (AOCI) - Change in Each Component of AOCI (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
Change in accumulated other comprehensive income (loss)
Balance, beginning of period				$ 226,143
Balance, end of period		$ 231,107	$ 233,021	231,107	$ 233,021
Net unrealized gains (losses) on investment securities
Change in accumulated other comprehensive income (loss)
Balance, beginning of period		(75)	1,127	(799)	(907)
Adjustment to opening balance, net of taxes						$ 504	$ 0
Adjusted balance, beginning of period						(295)	(907)
Other comprehensive income before reclassifications		101	1,025	435	3,051
Increase (decrease) due to amounts reclassified from AOCI		(128)	(98)	(242)	(90)
Total other comprehensive income		(27)	927	193	2,961
Balance, end of period		(102)	2,054	(102)	2,054
Debt valuation adjustment (DVA)
Change in accumulated other comprehensive income (loss)
Balance, beginning of period		(412)	178	(352)	0
Adjustment to opening balance, net of taxes						0	(15)
Adjusted balance, beginning of period						(352)	(15)
Other comprehensive income before reclassifications		(79)	16	(134)	208
Increase (decrease) due to amounts reclassified from AOCI		(5)	(4)	(10)	(3)
Total other comprehensive income		(84)	12	(144)	205
Balance, end of period		(496)	190	(496)	190
Cash flow hedges
Change in accumulated other comprehensive income (loss)
Balance, beginning of period		(562)	(300)	(560)	(617)
Adjustment to opening balance, net of taxes						0	0
Adjusted balance, beginning of period						(560)	(617)
Other comprehensive income before reclassifications		62	115	86	406
Increase (decrease) due to amounts reclassified from AOCI		55	36	29	62
Total other comprehensive income		117	151	115	468
Balance, end of period		(445)	(149)	(445)	(149)
Benefit plans
Change in accumulated other comprehensive income (loss)
Balance, beginning of period		(5,176)	(5,581)	(5,164)	(5,116)
Adjustment to opening balance, net of taxes						0	0
Adjusted balance, beginning of period						(5,164)	(5,116)
Other comprehensive income before reclassifications		(173)	(66)	(222)	(566)
Increase (decrease) due to amounts reclassified from AOCI		38	39	75	74
Total other comprehensive income		(135)	(27)	(147)	(492)
Balance, end of period		(5,311)	(5,608)	(5,311)	(5,608)
Foreign currency translation adjustment (CTA), net of hedges
Change in accumulated other comprehensive income (loss)
Balance, beginning of period		(24,188)	(22,050)	(25,506)	(22,704)
Adjustment to opening balance, net of taxes						0	0
Adjusted balance, beginning of period						(25,506)	(22,704)
Other comprehensive income before reclassifications		643	(552)	2,108	102
Increase (decrease) due to amounts reclassified from AOCI		0	0	(147)	0
Total other comprehensive income		643	(552)	1,961	102
Balance, end of period		(23,545)	(22,602)	(23,545)	(22,602)
Accumulated other comprehensive income (loss)
Change in accumulated other comprehensive income (loss)
Balance, beginning of period		(30,413)	(26,626)	(32,381)	(29,344)
Adjustment to opening balance, net of taxes	[1]					504	(15)
Adjusted balance, beginning of period						$ (31,877)	$ (29,359)
Other comprehensive income before reclassifications		554	538	2,273	3,201
Increase (decrease) due to amounts reclassified from AOCI		(40)	(27)	(295)	43
Total other comprehensive income		514	511	1,978	3,244
Balance, end of period		$ (29,899)	$ (26,115)	$ (29,899)	$ (26,115)

[1] See Note 1 to the Consolidated Financial Statements for additional details.