ACCOUNTING AND DISCLOSURE CHANGES - NARRATIVE (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2019	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash and restricted cash		$ 3,033	$ 1,672	$ 2,233		$ 4,394
Cash flows from investing activities		(3,206)	(3,079)	(4,743)
Cash flows from operating activities		$ 7,669	4,861	3,384
Accounting Standards Update 2018-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification of stranded tax effects	$ 58
Accounting Standards Update 2016-02 | Forecast | Subsequent Event | Low end of range
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right-of-use asset					$ 800
Lease liability					800
Accounting Standards Update 2016-02 | Forecast | Subsequent Event | High end of range
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right-of-use asset					1,000
Lease liability					$ 1,000
Accounting Standards Update 2016-18
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash and restricted cash				1,200		$ 4,400
Cash flows from financing activities				$ (1,200)
Accounting Standards Update 2016-15
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash flows from investing activities			135
Cash flows from operating activities			$ (135)