SHAREHOLDERS' EQUITY - Changes in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning of period	$ 6,615	$ 2,151
Adjusted balance, beginning of period	7,463
Other comprehensive income (loss) before reclassifications net of tax	(3,287)	2,340
Amounts reclassified from accumulated other comprehensive income net of tax	12	(10)
Other comprehensive income (loss), net of tax	(3,275)	2,330
Balance, end of period	4,188	4,481
Accounting Standards Update 2019-04
Accumulated Other Comprehensive Income [Roll Forward]
Amounts reclassified from accumulated other comprehensive income net of tax	848
Unrealized foreign currency translation gains (losses)
Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning of period	(1,623)	(1,847)
Adjusted balance, beginning of period	(1,623)
Other comprehensive income (loss) before reclassifications net of tax	80	(1)
Amounts reclassified from accumulated other comprehensive income net of tax	0	0
Other comprehensive income (loss), net of tax	80	(1)
Balance, end of period	(1,543)	(1,848)
Unrealized foreign currency translation gains (losses) | Accounting Standards Update 2019-04
Accumulated Other Comprehensive Income [Roll Forward]
Amounts reclassified from accumulated other comprehensive income net of tax	0
Unrealized gains (losses) on investment securities
Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning of period	8,548	4,234
Adjusted balance, beginning of period	9,396
Other comprehensive income (loss) before reclassifications net of tax	(3,359)	2,340
Amounts reclassified from accumulated other comprehensive income net of tax	6	(13)
Other comprehensive income (loss), net of tax	(3,353)	2,327
Balance, end of period	6,043	6,561
Unrealized gains (losses) on investment securities | Accounting Standards Update 2019-04
Accumulated Other Comprehensive Income [Roll Forward]
Amounts reclassified from accumulated other comprehensive income net of tax	848
Unrealized gains (losses) on derivatives
Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning of period	(33)	(24)
Adjusted balance, beginning of period	(33)
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	(35)	(26)
Unrealized gains (losses) on derivatives | Accounting Standards Update 2019-04
Accumulated Other Comprehensive Income [Roll Forward]
Amounts reclassified from accumulated other comprehensive income net of tax	0
Pension liability adjustment
Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning of period	(277)	(212)
Adjusted balance, beginning of period	(277)
Other comprehensive income (loss) before reclassifications net of tax	(6)	3
Amounts reclassified from accumulated other comprehensive income net of tax	6	3
Other comprehensive income (loss), net of tax	0	6
Balance, end of period	(277)	$ (206)
Pension liability adjustment | Accounting Standards Update 2019-04
Accumulated Other Comprehensive Income [Roll Forward]
Amounts reclassified from accumulated other comprehensive income net of tax	$ 0