RECLASSIFICATIONS OUT OF ACCUMULATED OTHER COMPREHENSIVE LOSS - Schedule of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	$ 20,270	$ 19,747
Other-than-temporary impairment not recognized in earnings on debt securities	(1)	(12)
Ending balance	20,059	19,847
Total AOCI
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(820)	(668)
Other comprehensive (loss) income before reclassifications	(324)	2
Other-than-temporary impairment not recognized in earnings on debt securities	(1)	(12)
Amounts reclassified from other comprehensive income (loss)	0	(5)
Net other comprehensive (loss) income	(325)	(15)
Ending balance	(1,145)	(683)
Net Unrealized (Losses) Gains on Derivatives
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(143)	(88)
Other comprehensive (loss) income before reclassifications	(52)	(3)
Other-than-temporary impairment not recognized in earnings on debt securities	0	0
Amounts reclassified from other comprehensive income (loss)	2	(6)
Net other comprehensive (loss) income	(50)	(9)
Ending balance	(193)	(97)
Net Unrealized (Losses) Gains on Debt Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(236)	(186)
Other comprehensive (loss) income before reclassifications	(272)	5
Other-than-temporary impairment not recognized in earnings on debt securities	(1)	(12)
Amounts reclassified from other comprehensive income (loss)	(5)	(2)
Net other comprehensive (loss) income	(278)	(9)
Ending balance	(514)	(195)
Employee Benefit Plans
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(441)	(394)
Other comprehensive (loss) income before reclassifications	0	0
Other-than-temporary impairment not recognized in earnings on debt securities	0	0
Amounts reclassified from other comprehensive income (loss)	3	3
Net other comprehensive (loss) income	3	3
Ending balance	$ (438)	$ (391)