GENERAL INFORMATION AND OTHER FINANCIAL DATA - EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017		Sep. 30, 2018	Sep. 30, 2017
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
(Losses) earnings attributable to common shares	$ 274	$ 57	[1]	$ 60	$ 757	[1]
Weighted-average common shares outstanding for basic EPS (in shares)	273,944,000	251,692,000	[1]	265,963,000	251,425,000	[1]
Dilutive effect of stock options, RSAs and RSUs (in shares)	854,000	1,672,000		736,000	1,562,000
Dilutive effect of common stock forward shares (in shares)	1,109,000	0		945,000	0
Weighted-average common shares outstanding for diluted EPS (in shares)	275,907,000	253,364,000	[1]	267,644,000	252,987,000	[1]
Basic earnings per common share	$ 1.00	$ 0.23	[1]	$ 0.23	$ 3.01	[1]
Diluted earnings per common share	$ 0.99	$ 0.22	[1]	$ 0.22	$ 2.99	[1]
Vested RSUs included in basic WASO	645,000	612,000		638,000	607,000
Convertible Preferred Stock [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Antidilutive securities excluded from earnings per share	19,152,109			15,863,530
Stock options, RSAs and RSUs [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Antidilutive securities excluded from earnings per share	508	2,608		1,552	2,608
Common Stock Forward Sales [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Antidilutive securities excluded from earnings per share	0			2,857,143
Performance-based RSUs [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Equity awards, granted (in shares)				358,363
Service-based RSUs [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Equity awards, granted (in shares)				266,990
IENova Plans [Member] | RSUs [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Equity awards, granted (in shares)				969,482

[1] As adjusted for the retrospective adoption of ASU 2017-07, which we discuss in Note 2, and a reclassification to conform to current year presentation, which we discuss in Note 1.