RECLASSIFICATIONS OUT OF ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Schedule of Accumulated Other Comprehensive (Loss) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		$ 20,270	$ 19,747	$ 19,646
Other comprehensive loss before reclassifications		(272)	(20)	(201)
Other-than-temporary impairment not recognized in earnings on debt securities		(3)	0	(17)
Amounts reclassified to the Consolidated Statements of Operations		(1)	13	(63)
Reclassification of tax effects resulting from the 2017 Tax Legislation			0
Net other comprehensive loss		(276)	(7)	(281)
Ending balance		20,817	20,270	19,747
Net Unrealized (Losses) Gains on Derivatives
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(143)	(88)	10
Other comprehensive loss before reclassifications		(33)	(14)	(62)
Other-than-temporary impairment not recognized in earnings on debt securities		0		0
Amounts reclassified to the Consolidated Statements of Operations		33	(16)	(36)
Reclassification of tax effects resulting from the 2017 Tax Legislation	[1]		(25)
Net other comprehensive loss		0	(30)	(98)
Ending balance		(143)	(143)	(88)
Net Unrealized (Losses) Gains on Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(236)	(186)	(28)
Other comprehensive loss before reclassifications		(239)	(6)	(139)
Other-than-temporary impairment not recognized in earnings on debt securities		(3)		(17)
Amounts reclassified to the Consolidated Statements of Operations		(12)	(2)	(2)
Reclassification of tax effects resulting from the 2017 Tax Legislation	[1]		(42)
Net other comprehensive loss		(254)	(8)	(158)
Ending balance		(490)	(236)	(186)
Employee Benefit Plans
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(441)	(394)	(369)
Other comprehensive loss before reclassifications		0	0	0
Other-than-temporary impairment not recognized in earnings on debt securities		0		0
Amounts reclassified to the Consolidated Statements of Operations		(22)	31	(25)
Reclassification of tax effects resulting from the 2017 Tax Legislation	[1]		(78)
Net other comprehensive loss		(22)	31	(25)
Ending balance		(463)	(441)	(394)
Total AOCI
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(820)	(668)	(387)
Reclassification of tax effects resulting from the 2017 Tax Legislation	[1]		(145)
Ending balance		$ (1,096)	$ (820)	$ (668)

[1] As of December 31, 2017, the balance of AOCI reflects the retrospective adoption of FASB ASU 2018-02, Income Statement-Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income. For further discussion, see Note 22 “Income Taxes.”