RECLASSIFICATIONS OUT OF ACCUMULATED OTHER COMPREHENSIVE LOSS - Schedule of Accumulated Other Comprehensive (Loss) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		$ 19,747	$ 19,646	$ 19,268
Other-than-temporary impairment not recognized in earnings on securities		0	(17)	(22)
Reclassification of tax effects resulting from the 2017 Tax Legislation		145
Ending balance		20,270	19,747	19,646
Net Unrealized (Losses) Gains on Derivatives
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(88)	10	(69)
Other comprehensive income before reclassifications		(14)	(62)	93
Other-than-temporary impairment not recognized in earnings on securities			0	0
Amounts reclassified from other comprehensive income		(16)	(36)	(14)
Net other comprehensive loss		(30)	(98)	79
Reclassification of tax effects resulting from the 2017 Tax Legislation	[1]	(25)
Ending balance		(143)	(88)	10
Net Unrealized (Losses) Gains on Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(186)	(28)	74
Other comprehensive income before reclassifications		(6)	(139)	(66)
Other-than-temporary impairment not recognized in earnings on securities			(17)	(22)
Amounts reclassified from other comprehensive income		(2)	(2)	(14)
Net other comprehensive loss		(8)	(158)	(102)
Reclassification of tax effects resulting from the 2017 Tax Legislation	[1]	(42)
Ending balance		(236)	(186)	(28)
Employee Benefit Plans
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(394)	(369)	(377)
Other comprehensive income before reclassifications		0	0	0
Other-than-temporary impairment not recognized in earnings on securities			0	0
Amounts reclassified from other comprehensive income		31	(25)	8
Net other comprehensive loss		31	(25)	8
Reclassification of tax effects resulting from the 2017 Tax Legislation	[1]	(78)
Ending balance		(441)	(394)	(369)
Total AOCI
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(668)	(387)	(372)
Other comprehensive income before reclassifications		(20)	(201)	27
Other-than-temporary impairment not recognized in earnings on securities			(17)	(22)
Amounts reclassified from other comprehensive income		13	(63)	(20)
Net other comprehensive loss		(7)	(281)	(15)
Reclassification of tax effects resulting from the 2017 Tax Legislation	[1]	(145)
Ending balance		$ (820)	$ (668)	$ (387)

[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.”