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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Change in accumulated other comprehensive income (loss)
Balance, beginning of period			$ 197,074
Balance, end of period	$ 198,110	$ 200,968	198,110	$ 200,968
Net unrealized gains (losses) on debt securities
Change in accumulated other comprehensive income (loss)
Balance, beginning of period	(1,115)	(2,219)	(2,250)	(1,158)
Adjustment to opening balance, net of taxes								$ (3)
Adjusted balance, beginning of period								(1,161)
Other comprehensive income before reclassifications	1,050	(433)	2,276	(1,383)
Increase (decrease) due to amounts reclassified from AOCI	(347)	(65)	(438)	(173)
Total other comprehensive income	703	(498)	1,838	(1,556)
Balance, end of period	(412)	(2,717)	(412)	(2,717)
Debt valuation adjustment (DVA)
Change in accumulated other comprehensive income (loss)
Balance, beginning of period	(379)	(793)	192	(921)
Adjustment to opening balance, net of taxes								0
Adjusted balance, beginning of period								(921)
Other comprehensive income before reclassifications	(14)	316	(589)	417
Increase (decrease) due to amounts reclassified from AOCI	17	2	21	29
Total other comprehensive income	3	318	(568)	446
Balance, end of period	(376)	(475)	(376)	(475)
Cash flow hedges
Change in accumulated other comprehensive income (loss)
Balance, beginning of period	(442)	(920)	(728)	(698)
Adjustment to opening balance, net of taxes								0
Adjusted balance, beginning of period								(698)
Other comprehensive income before reclassifications	414	(36)	600	(279)
Increase (decrease) due to amounts reclassified from AOCI	103	(65)	203	(44)
Total other comprehensive income	517	(101)	803	(323)
Balance, end of period	75	(1,021)	75	(1,021)
Benefit plans
Change in accumulated other comprehensive income (loss)
Balance, beginning of period	(6,321)	(6,095)	(6,257)	(6,183)
Adjustment to opening balance, net of taxes								0
Adjusted balance, beginning of period								(6,183)
Other comprehensive income before reclassifications	(305)	261	(415)	302
Increase (decrease) due to amounts reclassified from AOCI	52	40	98	87
Total other comprehensive income	(253)	301	(317)	389
Balance, end of period	(6,574)	(5,794)	(6,574)	(5,794)
Foreign currency translation adjustment (CTA), net of hedges
Change in accumulated other comprehensive income (loss)
Balance, beginning of period	(28,012)	(24,588)	(28,070)	(25,708)
Adjustment to opening balance, net of taxes								0
Adjusted balance, beginning of period								(25,708)
Other comprehensive income before reclassifications	91	(2,867)	149	(1,747)
Increase (decrease) due to amounts reclassified from AOCI	0	0	0	0
Total other comprehensive income	91	(2,867)	149	(1,747)
Balance, end of period	(27,921)	(27,455)	(27,921)	(27,455)
Excluded component of fair value hedges
Change in accumulated other comprehensive income (loss)
Balance, beginning of period	(39)	(4)	(57)	0
Adjustment to opening balance, net of taxes								0
Adjusted balance, beginning of period								0
Other comprehensive income before reclassifications	44	(28)	62	(32)
Increase (decrease) due to amounts reclassified from AOCI	0	0	0	0
Total other comprehensive income	44	(28)	62	(32)
Balance, end of period	5	(32)	5	(32)
Accumulated other comprehensive income (loss)
Change in accumulated other comprehensive income (loss)
Balance, beginning of period	(36,308)	(34,619)	(37,170)	(34,668)
Adjustment to opening balance, net of taxes					$ 0	$ 0	$ 0	(3)	$ (3)
Adjusted balance, beginning of period					$ (36,308)	$ (37,170)	$ (34,619)	$ (34,671)	$ (34,671)
Other comprehensive income before reclassifications	1,280	(2,787)	2,083	(2,722)
Increase (decrease) due to amounts reclassified from AOCI	(175)	(88)	(116)	(101)
Total other comprehensive income	1,105	(2,875)	1,967	(2,823)
Balance, end of period	$ (35,203)	$ (37,494)	$ (35,203)	$ (37,494)