ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Schedule of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Jan. 02, 2019	Jan. 01, 2019
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	$ 22,201	$ 20,817
Other comprehensive income before reclassifications	496	285
Amounts reclassified to the Consolidated Statements of Operations	0	13
Net other comprehensive income	496	298
Cumulative effect of change in accounting principle			$ (331)	$ 17
Ending balance	21,950	21,531
Total AOCI
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(411)	(1,096)
Net other comprehensive income	496	298
Cumulative effect of change in accounting principle			$ 0	5
Ending balance	85	(793)
Net Unrealized (Losses) Gains on Derivatives
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	3	(143)
Other comprehensive income before reclassifications	96	39
Amounts reclassified to the Consolidated Statements of Operations	(3)	15
Net other comprehensive income	93	54
Cumulative effect of change in accounting principle				0
Ending balance	96	(89)
Net Unrealized (Losses) Gains on Debt Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	1	(490)
Other comprehensive income before reclassifications	400	246
Amounts reclassified to the Consolidated Statements of Operations	0	(5)
Net other comprehensive income	400	241
Cumulative effect of change in accounting principle				5
Ending balance	401	(244)
Employee Benefit Plans
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(415)	(463)
Other comprehensive income before reclassifications	0	0
Amounts reclassified to the Consolidated Statements of Operations	3	3
Net other comprehensive income	3	3
Cumulative effect of change in accounting principle				$ 0
Ending balance	$ (412)	$ (460)