SHAREHOLDERS' EQUITY - Changes in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018		Jun. 30, 2017
Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning of period	[1]	$ 3,685	$ 2,632	$ 4,028		$ 2,630
Other comprehensive income loss before reclassifications net of tax	[1]	(857)	765	(1,426)	[2]	755
Amounts reclassified from accumulated other comprehensive income net of tax	[1]	24	4	24		16
Other comprehensive income (loss), net of tax	[1]	(833)	769	(1,402)		771
Balance, end of period	[1]	2,852	3,401	2,852		3,401
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]	(1,303)	(1,650)	(1,750)		(1,983)
Other comprehensive income loss before reclassifications net of tax	[1]	(463)	70	309	[2]	403
Amounts reclassified from accumulated other comprehensive income net of tax	[1]	0	0	0		0
Other comprehensive income (loss), net of tax	[1]	(463)	70	309		403
Balance, end of period	[1]	(1,766)	(1,580)	(1,766)		(1,580)
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]	5,206	4,474	5,964		4,805
Other comprehensive income loss before reclassifications net of tax	[1]	(391)	698	(1,733)	[2]	357
Amounts reclassified from accumulated other comprehensive income net of tax	[1]	21	1	19		11
Other comprehensive income (loss), net of tax	[1]	(370)	699	(1,714)		368
Balance, end of period	[1]	4,836	5,173	4,836		5,173
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]	(21)	(22)	(23)		(24)
Other comprehensive income loss before reclassifications net of tax	[1]	(2)	(1)	3	[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]	(2)	(1)	3		1
Balance, end of period	[1]	(23)	(23)	(23)		(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]	(197)	(170)	(163)		(168)
Other comprehensive income loss before reclassifications net of tax	[1]	(1)	(2)	(5)	[2]	(6)
Amounts reclassified from accumulated other comprehensive income net of tax	[1]	3	3	5		5
Other comprehensive income (loss), net of tax	[1]	2	1	0		(1)
Balance, end of period	[1]	$ (195)	$ (169)	(195)		$ (169)
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.

[2] Amounts have been corrected to exclude the cumulative effects of changes in accounting principles for financial instruments and the tax effects from tax reform as identified in the rollforward of Accumulated Other Comprehensive Income within the Consolidated Statements of Shareholder’s Equity.