SHAREHOLDERS' EQUITY - Changes in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 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		$ 2,151	$ 4,028
Other comprehensive income (loss) before reclassifications net of tax		2,340	(571)
Amounts reclassified from accumulated other comprehensive income net of tax		(10)	228
Other comprehensive income (loss), net of tax		2,330	(343)
Balance, end of period		4,481	3,685
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
Accumulated other comprehensive income (loss) | Accounting Standards Update 2016-01
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Cumulative effect of change in accounting principle, net of income taxes			(148)
Accumulated other comprehensive income (loss) | Accounting Standards Update 2018-02
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Cumulative effect of change in accounting principle, net of income taxes			374
Unrealized foreign currency translation gains (losses)
Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning of period		(1,847)	(1,750)
Other comprehensive income (loss) before reclassifications net of tax		(1)	447
Amounts reclassified from accumulated other comprehensive income net of tax		0	0
Other comprehensive income (loss), net of tax		(1)	447
Balance, end of period		(1,848)	(1,303)
Unrealized gains (losses) on investment securities
Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning of period		4,234	5,964
Other comprehensive income (loss) before reclassifications net of tax		2,340	(983)
Amounts reclassified from accumulated other comprehensive income net of tax		(13)	225	[2]
Other comprehensive income (loss), net of tax		2,327	(758)
Balance, end of period		6,561	5,206
Unrealized gains (losses) on derivatives
Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning of period		(24)	(23)
Other comprehensive income (loss) before reclassifications net of tax		(2)	2
Amounts reclassified from accumulated other comprehensive income net of tax		0	0
Other comprehensive income (loss), net of tax		(2)	2
Balance, end of period		(26)	(21)
Pension liability adjustment
Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning of period		(212)	(163)
Other comprehensive income (loss) before reclassifications net of tax		3	(37)
Amounts reclassified from accumulated other comprehensive income net of tax		3	3
Other comprehensive income (loss), net of tax		6	(34)
Balance, end of period		$ (206)	$ (197)

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

[2] Includes amounts reclassified due to changes in accounting principles of $(148) related to financial instruments and $374 related to tax effects from tax reform