CHANGES IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (AOCI) - Change in Each Component of AOCI (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 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		$ 228,622	$ 232,690	228,622	$ 232,690
Net unrealized gains (losses) on investment securities
Change in accumulated other comprehensive income (loss)
Balance, beginning of period		(102)	2,054	(799)	(907)
Adjustment to opening balance, net of taxes						$ 504	$ 0
Adjusted balance, beginning of period						(295)	(907)
Other comprehensive income before reclassifications		60	(270)	495	2,781
Increase (decrease) due to amounts reclassified from AOCI		(126)	(162)	(368)	(252)
Total other comprehensive income		(66)	(432)	127	2,529
Balance, end of period		(168)	1,622	(168)	1,622
Debt valuation adjustment (DVA)
Change in accumulated other comprehensive income (loss)
Balance, beginning of period		(496)	190	(352)	0
Adjustment to opening balance, net of taxes						0	(15)
Adjusted balance, beginning of period						(352)	(15)
Other comprehensive income before reclassifications		(125)	(197)	(259)	11
Increase (decrease) due to amounts reclassified from AOCI		2	(3)	(8)	(6)
Total other comprehensive income		(123)	(200)	(267)	5
Balance, end of period		(619)	(10)	(619)	(10)
Cash flow hedges
Change in accumulated other comprehensive income (loss)
Balance, beginning of period		(445)	(149)	(560)	(617)
Adjustment to opening balance, net of taxes						0	0
Adjusted balance, beginning of period						(560)	(617)
Other comprehensive income before reclassifications		(27)	(136)	59	270
Increase (decrease) due to amounts reclassified from AOCI		35	53	64	115
Total other comprehensive income		8	(83)	123	385
Balance, end of period		(437)	(232)	(437)	(232)
Benefit plans
Change in accumulated other comprehensive income (loss)
Balance, beginning of period		(5,311)	(5,608)	(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		(71)	(28)	(293)	(594)
Increase (decrease) due to amounts reclassified from AOCI		42	40	117	114
Total other comprehensive income		(29)	12	(176)	(480)
Balance, end of period		(5,340)	(5,596)	(5,340)	(5,596)
Foreign currency translation adjustment (CTA), net of hedges
Change in accumulated other comprehensive income (loss)
Balance, beginning of period		(23,545)	(22,602)	(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		218	(375)	2,326	(273)
Increase (decrease) due to amounts reclassified from AOCI		0	0	(147)	0
Total other comprehensive income		218	(375)	2,179	(273)
Balance, end of period		(23,327)	(22,977)	(23,327)	(22,977)
Accumulated other comprehensive income (loss)
Change in accumulated other comprehensive income (loss)
Balance, beginning of period		(29,899)	(26,115)	(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		55	(1,006)	2,328	2,195
Increase (decrease) due to amounts reclassified from AOCI		(47)	(72)	(342)	(29)
Total other comprehensive income		8	(1,078)	1,986	2,166
Balance, end of period		$ (29,891)	$ (27,193)	$ (29,891)	$ (27,193)

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