ACCUMULATED OTHER COMPREHENSIVE INCOME - Summary of Changes in AOCI by Component (Detail) - USD ($) $ in Millions	3 Months Ended				6 Months Ended		12 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019	Jan. 01, 2018
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning of year	$ 7,593	$ 7,866	$ 9,062	$ 9,109	$ 7,866	$ 9,109	$ 7,866	$ 9,109	$ 8,221
Adoption of new accounting standard										$ (161)	$ (3)
Other comprehensive (loss) income before reclassifications							(315)	(347)
Amounts reclassified from AOCI							589	66
Total other comprehensive income (loss), net of tax	4	98	329	(115)	102	214	(274)	281	(722)
End of year	$ 7,803	7,593	$ 8,830	9,062	7,803	8,830	7,912	7,866	9,109
CTA
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning of year		(2,868)		(2,545)	(2,868)	(2,545)	(2,868)	(2,545)
Adoption of new accounting standard										9	0
Other comprehensive (loss) income before reclassifications							(95)	(323)
Amounts reclassified from AOCI							0	0
Total other comprehensive income (loss), net of tax							95	323
End of year							(2,954)	(2,868)	(2,545)
Pension and other employee benefits
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning of year		(954)		(987)	(954)	(987)	(954)	(987)
Adoption of new accounting standard										(169)	0
Other comprehensive (loss) income before reclassifications							(184)	(23)
Amounts reclassified from AOCI							592	56
Total other comprehensive income (loss), net of tax							(408)	(33)
End of year							(715)	(954)	(987)
Hedging activities
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning of year		(1)			(1)		(1)
Adoption of new accounting standard										$ (1)
Other comprehensive (loss) income before reclassifications							(36)
Amounts reclassified from AOCI							(3)
Total other comprehensive income (loss), net of tax							39
End of year							(41)	(1)
Hedging activities
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning of year		(1)		(10)	(1)	(10)	(1)	(10)
Adoption of new accounting standard											0
Other comprehensive (loss) income before reclassifications								(1)
Amounts reclassified from AOCI								10
Total other comprehensive income (loss), net of tax								(9)
End of year								(1)	(10)
Available-for-sale securities
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning of year		0		3	0	3	0	3
Adoption of new accounting standard											$ (3)
Other comprehensive (loss) income before reclassifications								0
Amounts reclassified from AOCI								0
Total other comprehensive income (loss), net of tax								0
End of year								0	3
Accumulated Other Comprehensive Income (Loss)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning of year		$ (3,823)		$ (3,539)	$ (3,823)	$ (3,539)	(3,823)	(3,539)
End of year							$ (3,710)	$ (3,823)	$ (3,539)