SHAREHOLDERS' EQUITY - Changes in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Cumulative effect of change in accounting principle, net of income taxes	[1]					$ 0
Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning of period		$ 4,481	$ 3,685	$ 2,151	$ 4,028
Other comprehensive income (loss) before reclassifications net of tax		1,899	(857)	4,240	(1,426)
Amounts reclassified from accumulated other comprehensive income net of tax		(16)	24	(27)	24
Other comprehensive income (loss), net of tax		1,883	(833)	4,213	(1,402)
Balance, end of period		6,364	2,852	6,364	2,852
Accounting Standards Update 2016-01
Accumulated Other Comprehensive Income [Roll Forward]
Amounts reclassified from accumulated other comprehensive income net of tax					(148)
Accounting Standards Update 2018-02
Accumulated Other Comprehensive Income [Roll Forward]
Amounts reclassified from accumulated other comprehensive income net of tax					374
Accumulated other comprehensive income (loss)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Cumulative effect of change in accounting principle, net of income taxes	[1]					$ 226
Unrealized foreign currency translation gains (losses)
Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning of period		(1,848)	(1,303)	(1,847)	(1,750)
Other comprehensive income (loss) before reclassifications net of tax		393	(463)	392	309
Amounts reclassified from accumulated other comprehensive income net of tax		0	0	0	0
Other comprehensive income (loss), net of tax		393	(463)	392	309
Balance, end of period		(1,455)	(1,766)	(1,455)	(1,766)
Unrealized foreign currency translation gains (losses) | Accounting Standards Update 2016-01
Accumulated Other Comprehensive Income [Roll Forward]
Amounts reclassified from accumulated other comprehensive income net of tax					0
Unrealized foreign currency translation gains (losses) | Accounting Standards Update 2018-02
Accumulated Other Comprehensive Income [Roll Forward]
Amounts reclassified from accumulated other comprehensive income net of tax					(325)
Unrealized gains (losses) on investment securities
Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning of period		6,561	5,206	4,234	5,964
Other comprehensive income (loss) before reclassifications net of tax		1,512	(391)	3,853	(1,733)
Amounts reclassified from accumulated other comprehensive income net of tax		(18)	21	(32)	19
Other comprehensive income (loss), net of tax		1,494	(370)	3,821	(1,714)
Balance, end of period		8,055	4,836	8,055	4,836
Unrealized gains (losses) on investment securities | Accounting Standards Update 2016-01
Accumulated Other Comprehensive Income [Roll Forward]
Amounts reclassified from accumulated other comprehensive income net of tax					(148)
Unrealized gains (losses) on investment securities | Accounting Standards Update 2018-02
Accumulated Other Comprehensive Income [Roll Forward]
Amounts reclassified from accumulated other comprehensive income net of tax					734
Unrealized gains (losses) on derivatives
Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning of period		(26)	(21)	(24)	(23)
Other comprehensive income (loss) before reclassifications net of tax		(1)	(2)	(3)	3
Amounts reclassified from accumulated other comprehensive income net of tax		0	0	0	0
Other comprehensive income (loss), net of tax		(1)	(2)	(3)	3
Balance, end of period		(27)	(23)	(27)	(23)
Unrealized gains (losses) on derivatives | Accounting Standards Update 2016-01
Accumulated Other Comprehensive Income [Roll Forward]
Amounts reclassified from accumulated other comprehensive income net of tax					0
Unrealized gains (losses) on derivatives | Accounting Standards Update 2018-02
Accumulated Other Comprehensive Income [Roll Forward]
Amounts reclassified from accumulated other comprehensive income net of tax					(3)
Pension liability adjustment
Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning of period		(206)	(197)	(212)	(163)
Other comprehensive income (loss) before reclassifications net of tax		(5)	(1)	(2)	(5)
Amounts reclassified from accumulated other comprehensive income net of tax		2	3	5	5
Other comprehensive income (loss), net of tax		(3)	2	3	0
Balance, end of period		$ (209)	$ (195)	$ (209)	(195)
Pension liability adjustment | Accounting Standards Update 2016-01
Accumulated Other Comprehensive Income [Roll Forward]
Amounts reclassified from accumulated other comprehensive income net of tax					0
Pension liability adjustment | Accounting Standards Update 2018-02
Accumulated Other Comprehensive Income [Roll Forward]
Amounts reclassified from accumulated other comprehensive income net of tax					$ (32)

[1] See Note 1 of the Notes to the Consolidated Financial Statements in the Company's 2018 Annual Report on Form 10-K