GUARANTOR FINANCIAL INFORMATION - Condensed Consolidating Statement of Cash Flows (Details) - USD ($) $ in Millions	6 Months Ended			12 Months Ended
	Jun. 30, 2018		Jun. 30, 2017	Dec. 31, 2017
Cash flows – operating activities
Cash from (used for) operating activities - continuing operations	$ 2,240		$ 2,930
Cash from (used for) operating activities - discontinued operations	(293)		(895)
Cash from (used for) operating activities	1,947		2,035
Cash flows – investing activities
Cash from (used for) investing activities – continuing operations	2,665		4,397
Cash from (used for) investing activities – continuing operations	151		(2,089)
Cash from (used for) investing activities	2,816		2,309
Cash flows – financing activities
Cash from (used for) financing activities – continuing operations	(20,913)		(12,089)
Cash from (used for) financing activities – discontinued operations	0		1,909
Cash from (used for) financing activities	(20,913)		(10,181)
Effect of currency exchange rate changes on cash, cash equivalents and restricted cash	(285)		538
Increase (decrease) in cash, cash equivalents and restricted cash	(16,436)		(5,299)
Cash, cash equivalents and restricted cash at beginning of year	44,724		50,384	$ 50,384
Cash, cash equivalents and restricted cash at June 30	28,288		45,085	44,724
Less cash, cash equivalents and restricted cash of discontinued operations at June 30	615		526
Cash, cash equivalents and restricted cash of continuing operations at June 30	27,674	[1]	44,559	43,967	[1]
Reportable Legal Entities
Cash flows – operating activities
Cash from (used for) operating activities - continuing operations	(927)		5,550
Cash flows – investing activities
Cash from (used for) investing activities – continuing operations	5,696		3,190
Cash flows – financing activities
Cash from (used for) financing activities – continuing operations	(20,778)		(13,502)
Reportable Legal Entities | Parent Company Guarantor
Cash flows – operating activities
Cash from (used for) operating activities - continuing operations	12,625		10,330
Cash from (used for) operating activities - discontinued operations	(1,673)		(388)
Cash from (used for) operating activities	10,952		9,942
Cash flows – investing activities
Cash from (used for) investing activities – continuing operations	12,523		(24,692)
Cash from (used for) investing activities – continuing operations	0		0
Cash from (used for) investing activities	12,523		(24,692)
Cash flows – financing activities
Cash from (used for) financing activities – continuing operations	(25,094)		16,447
Cash from (used for) financing activities – discontinued operations	0		0
Cash from (used for) financing activities	(25,094)		16,447
Effect of currency exchange rate changes on cash, cash equivalents and restricted cash	0		0
Increase (decrease) in cash, cash equivalents and restricted cash	(1,620)		1,697
Cash, cash equivalents and restricted cash at beginning of year	3,472		2,729	2,729
Cash, cash equivalents and restricted cash at June 30	1,852		4,426	3,472
Less cash, cash equivalents and restricted cash of discontinued operations at June 30	0		0
Cash, cash equivalents and restricted cash of continuing operations at June 30	1,852		4,426	3,472
Reportable Legal Entities | Subsidiary Issuer
Cash flows – operating activities
Cash from (used for) operating activities - continuing operations	(268)		25
Cash from (used for) operating activities - discontinued operations	0		0
Cash from (used for) operating activities	(268)		25
Cash flows – investing activities
Cash from (used for) investing activities – continuing operations	268		(25)
Cash from (used for) investing activities – continuing operations	0		0
Cash from (used for) investing activities	268		(25)
Cash flows – financing activities
Cash from (used for) financing activities – continuing operations	0		0
Cash from (used for) financing activities – discontinued operations	0		0
Cash from (used for) financing activities	0		0
Effect of currency exchange rate changes on cash, cash equivalents and restricted cash	0		0
Increase (decrease) in cash, cash equivalents and restricted cash	0		0
Cash, cash equivalents and restricted cash at beginning of year	0		0	0
Cash, cash equivalents and restricted cash at June 30	0		0	0
Less cash, cash equivalents and restricted cash of discontinued operations at June 30	0		0
Cash, cash equivalents and restricted cash of continuing operations at June 30	0		0	0
Reportable Legal Entities | Subsidiary Guarantor
Cash flows – operating activities
Cash from (used for) operating activities - continuing operations	(117)		225
Cash from (used for) operating activities - discontinued operations	0		0
Cash from (used for) operating activities	(117)		225
Cash flows – investing activities
Cash from (used for) investing activities – continuing operations	(882)		608
Cash from (used for) investing activities – continuing operations	0		0
Cash from (used for) investing activities	(882)		608
Cash flows – financing activities
Cash from (used for) financing activities – continuing operations	999		(833)
Cash from (used for) financing activities – discontinued operations	0		0
Cash from (used for) financing activities	999		(833)
Effect of currency exchange rate changes on cash, cash equivalents and restricted cash	0		0
Increase (decrease) in cash, cash equivalents and restricted cash	0		1
Cash, cash equivalents and restricted cash at beginning of year	3		41	41
Cash, cash equivalents and restricted cash at June 30	3		42	3
Less cash, cash equivalents and restricted cash of discontinued operations at June 30	0		0
Cash, cash equivalents and restricted cash of continuing operations at June 30	3		42	3
Reportable Legal Entities | Non- Guarantor Subsidiaries
Cash flows – operating activities
Cash from (used for) operating activities - continuing operations	8,330		105,269
Cash from (used for) operating activities - discontinued operations	1,381		(507)
Cash from (used for) operating activities	9,711		104,761
Cash flows – investing activities
Cash from (used for) investing activities – continuing operations	(22,097)		(52,457)
Cash from (used for) investing activities – continuing operations	151		(2,089)
Cash from (used for) investing activities	(21,946)		(54,545)
Cash flows – financing activities
Cash from (used for) financing activities – continuing operations	(2,406)		(60,697)
Cash from (used for) financing activities – discontinued operations	0		1,909
Cash from (used for) financing activities	(2,406)		(58,789)
Effect of currency exchange rate changes on cash, cash equivalents and restricted cash	(285)		538
Increase (decrease) in cash, cash equivalents and restricted cash	(14,926)		(8,035)
Cash, cash equivalents and restricted cash at beginning of year	41,993		49,204	49,204
Cash, cash equivalents and restricted cash at June 30	27,067		41,169	41,993
Less cash, cash equivalents and restricted cash of discontinued operations at June 30	615		526
Cash, cash equivalents and restricted cash of continuing operations at June 30	26,452		40,643	41,236
Consolidating Adjustments
Cash flows – operating activities
Cash from (used for) operating activities - continuing operations	(18,330)		(112,919)
Cash from (used for) operating activities - discontinued operations	(1)		0
Cash from (used for) operating activities	(18,331)		(112,919)
Cash flows – investing activities
Cash from (used for) investing activities – continuing operations	12,852		80,963
Cash from (used for) investing activities – continuing operations	0		0
Cash from (used for) investing activities	12,852		80,963
Cash flows – financing activities
Cash from (used for) financing activities – continuing operations	5,588		32,994
Cash from (used for) financing activities – discontinued operations	0		0
Cash from (used for) financing activities	5,588		32,994
Effect of currency exchange rate changes on cash, cash equivalents and restricted cash	0		0
Increase (decrease) in cash, cash equivalents and restricted cash	110		1,037
Cash, cash equivalents and restricted cash at beginning of year	(743)		(1,590)	(1,590)
Cash, cash equivalents and restricted cash at June 30	(634)		(552)	(743)
Less cash, cash equivalents and restricted cash of discontinued operations at June 30	0		0
Cash, cash equivalents and restricted cash of continuing operations at June 30	$ (634)		$ (552)	$ (743)

[1] Includes restricted cash of $725 million and $668 million at June 30, 2018 and December 31, 2017, respectively.