SHAREHOLDERS' EQUITY - Changes in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning of period	[1]	$ 4,028	$ 2,630	$ 625
Other comprehensive income loss before reclassifications net of tax	[1]	(2,150)	1,386	2,037
Amounts reclassified from accumulated other comprehensive income net of tax	[1]	47	12	(32)
Other comprehensive income (loss), net of tax	[1]	(2,103)	1,398	2,005
Balance, end of period	[1]	2,151	4,028	2,630
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]	(1,750)	(1,983)	(2,196)
Other comprehensive income loss before reclassifications net of tax	[1]	228	233	213
Amounts reclassified from accumulated other comprehensive income net of tax	[1]	0	0	0
Other comprehensive income (loss), net of tax	[1]	228	233	213
Balance, end of period	[1]	(1,847)	(1,750)	(1,983)
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]	5,964	4,805	2,986
Other comprehensive income loss before reclassifications net of tax	[1]	(2,350)	1,158	1,854
Amounts reclassified from accumulated other comprehensive income net of tax	[1]	34	1	(35)
Other comprehensive income (loss), net of tax	[1]	(2,316)	1,159	1,819
Balance, end of period	[1]	4,234	5,964	4,805
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)	(24)	(26)
Other comprehensive income loss before reclassifications net of tax	[1]	2	1	2
Amounts reclassified from accumulated other comprehensive income net of tax	[1]	0	0	0
Other comprehensive income (loss), net of tax	[1]	2	1	2
Balance, end of period	[1]	(24)	(23)	(24)
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]	(163)	(168)	(139)
Other comprehensive income loss before reclassifications net of tax	[1]	(30)	(6)	(32)
Amounts reclassified from accumulated other comprehensive income net of tax	[1]	13	11	3
Other comprehensive income (loss), net of tax	[1]	(17)	5	(29)
Balance, end of period	[1]	(212)	$ (163)	$ (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.