BASIS OF PRESENTATION AND ACCOUNTING CHANGES - Accounting Changes (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended		12 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Jun. 30, 2018	Jan. 01, 2018	Jun. 30, 2017	Jan. 01, 2017	Dec. 31, 2016	Jan. 01, 2016
New Accounting Pronouncements or Change in Accounting Principle
Revenue		$ 18,389	$ 18,419	$ 55,730	$ 54,940
Operating expenses		10,311	10,417	31,948	31,900
Decrease in retained earnings		(148,436)		(148,436)		$ (138,425)
Available for sale debt securities		284,782		284,782		290,725
Held to maturity securities		53,249		53,249		53,320
Reclassification into AOCI		(38,645)		(38,645)		(34,668)
Net cash used in investing activities of continuing operations				(56,563)	(43,460)
Net reduction to total stockholders' equity		(197,863)	(228,622)	(197,863)	(228,622)	(201,672)
Accounting Standards Update 2016-16
New Accounting Pronouncements or Change in Accounting Principle
Increase in DTAs								$ 300
Decrease in retained earnings								80
Decrease in prepaid taxes								380
Accounting Standards Update 2017-12
New Accounting Pronouncements or Change in Accounting Principle
Available for sale debt securities								4,000
Held to maturity securities								(4,000)
Accounting Standards Update 2016-01
New Accounting Pronouncements or Change in Accounting Principle
Decrease in retained earnings												$ 15
Reclassification into AOCI												$ 15
Accounting Standards Update 2016-01 And 2018-03
New Accounting Pronouncements or Change in Accounting Principle
Cumulative effect adjustment after tax								$ 3
Accounting Standards Update 2016-18
New Accounting Pronouncements or Change in Accounting Principle
Net cash used in investing activities of continuing operations					26,100
Early adoption | Accounting Standards Update 2017-08
New Accounting Pronouncements or Change in Accounting Principle
Net reduction to total stockholders' equity										$ 156
Retained earnings
New Accounting Pronouncements or Change in Accounting Principle
Cumulative effect adjustment after tax	[1]					(84)	$ 0		$ 0		$ (660)
Net reduction to total stockholders' equity		(148,436)	(155,174)	(148,436)	(155,174)	(138,425)	(145,211)		(152,178)		(146,477)
Retained earnings | Early adoption | Accounting Standards Update 2017-08
New Accounting Pronouncements or Change in Accounting Principle
Cumulative effect adjustment after tax										(660)
Accumulated other comprehensive income (loss)
New Accounting Pronouncements or Change in Accounting Principle
Cumulative effect adjustment after tax	[1]					(3)	0		0		504
Net reduction to total stockholders' equity		38,645	$ 29,891	38,645	$ 29,891	34,668	$ 37,494		$ 29,899		$ 32,381
Accumulated other comprehensive income (loss) | Early adoption | Accounting Standards Update 2017-08
New Accounting Pronouncements or Change in Accounting Principle
Cumulative effect adjustment after tax										$ 504
Restatement Adjustment | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle
Revenue		250		750		1,000
Operating expenses		$ 250		$ 750		$ 1,000

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