SHAREHOLDERS' EQUITY - Changes in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning of period	[1]	$ 2,852	$ 3,401	$ 4,028	$ 2,630
Other comprehensive income loss before reclassifications net of tax	[1]	(919)	159	(2,345)	914
Amounts reclassified from accumulated other comprehensive income net of tax	[1]	(24)	(29)	0	(13)
Other comprehensive income (loss), net of tax	[1]	(943)	130	(2,345)	901
Balance, end of period	[1]	1,909	3,531	1,909	3,531
Accounting Standards Update 2016-01
Accumulated Other Comprehensive Income [Roll Forward]
Amounts reclassified from accumulated other comprehensive income net of tax	[1]			(148)
Accounting Standards Update 2018-02
Accumulated Other Comprehensive Income [Roll Forward]
Amounts reclassified from accumulated other comprehensive income net of tax	[1]			374
Unrealized foreign currency translation gains (losses)
Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning of period	[1]	(1,766)	(1,580)	(1,750)	(1,983)
Other comprehensive income loss before reclassifications net of tax	[1]	(347)	(135)	(38)	268
Amounts reclassified from accumulated other comprehensive income net of tax	[1]	0	0	0	0
Other comprehensive income (loss), net of tax	[1]	(347)	(135)	(38)	268
Balance, end of period	[1]	(2,113)	(1,715)	(2,113)	(1,715)
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	[1]			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	[1]			(325)
Unrealized gains (losses) on investment securities
Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning of period	[1]	4,836	5,173	5,964	4,805
Other comprehensive income loss before reclassifications net of tax	[1]	(569)	296	(2,302)	653
Amounts reclassified from accumulated other comprehensive income net of tax	[1]	(27)	(32)	(8)	(21)
Other comprehensive income (loss), net of tax	[1]	(596)	264	(2,310)	632
Balance, end of period	[1]	4,240	5,437	4,240	5,437
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	[1]			(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	[1]			734
Unrealized gains (losses) on derivatives
Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning of period	[1]	(23)	(23)	(23)	(24)
Other comprehensive income loss before reclassifications net of tax	[1]	(1)	0	2	1
Amounts reclassified from accumulated other comprehensive income net of tax	[1]	0	0	0	0
Other comprehensive income (loss), net of tax	[1]	(1)	0	2	1
Balance, end of period	[1]	(24)	(23)	(24)	(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	[1]			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	[1]			(3)
Pension liability adjustment
Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning of period	[1]	(195)	(169)	(163)	(168)
Other comprehensive income loss before reclassifications net of tax	[1]	(2)	(2)	(7)	(8)
Amounts reclassified from accumulated other comprehensive income net of tax	[1]	3	3	8	8
Other comprehensive income (loss), net of tax	[1]	1	1	1	0
Balance, end of period	[1]	$ (194)	$ (168)	(194)	$ (168)
Pension liability adjustment | Accounting Standards Update 2016-01
Accumulated Other Comprehensive Income [Roll Forward]
Amounts reclassified from accumulated other comprehensive income net of tax	[1]			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	[1]			$ (32)

[1] All amounts in the table above are net of tax.