GENERAL INFORMATION AND OTHER FINANCIAL DATA - EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017		Jun. 30, 2018	Jun. 30, 2017
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
(Losses) earnings attributable to common shares	$ (561)	$ 259	[1]	$ (214)	$ 700	[1]
Weighted-average common shares outstanding for basic EPS (in shares)	265,837,000	251,447,000	[1]	261,906,000	251,290,000	[1]
Dilutive effect of stock options, RSAs and RSUs (in shares)	0	1,375,000		0	1,319,000
Dilutive effect of common stock forward shares (in shares)	0	0		0	0
Weighted-average common shares outstanding for diluted EPS (in shares)	265,837,000	252,822,000	[1]	261,906,000	252,609,000	[1]
Basic (losses) earnings per common share	$ (2.11)	$ 1.03	[1]	$ (0.82)	$ 2.79	[1]
Diluted (losses) earnings per common share	$ (2.11)	$ 1.03	[1]	$ (0.82)	$ 2.77	[1]
Vested RSUs included in basic WASO	640,000	608,000		634,000	604,000
Convertible Preferred Stock [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Antidilutive securities excluded from earnings per share	15,296,567
Stock options, RSAs and RSUs [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Antidilutive securities excluded from earnings per share	1,816	3,010		1,816	3,010
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)	266,569
IENova Plans [Member] | RSUs [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Equity awards, granted (in shares)	966,747
Treasury Stock Method [Member] | Stock options, RSAs and RSUs [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Antidilutive securities excluded from earnings per share	986,000			931,000
Treasury Stock Method [Member] | Common Stock Forward Sales [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Antidilutive securities excluded from earnings per share	714,000			746,000

[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.