EARNINGS PER COMMON SHARE - Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended						6 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share [Abstract]
Weighted average number of shares outstanding - basic (in shares)	447.5			490.4					453.0	499.8
Effect of dilutive securities common shares, employee stock awards (in shares)	0.0			0.0					1.1	0.0
Weighted average common shares outstanding - diluted (in shares)	447.5			490.4					454.1	499.8
Net income (loss)	$ (705)	$ (3,933)	$ 5,425	$ (306)	$ 428	$ (739)	$ 1,492	$ (311)	$ 787	$ (617)	$ (1,467)	$ 2,189	$ 1,201
Less: Net income (loss) attributable to the noncontrolling interest	74			68					197	201
Net income (loss) attributable to Holdings	(779)	$ (4,019)	$ 5,388	(374)	$ 361	$ (805)	$ 1,369	$ (444)	590	(818)	$ (1,764)	$ 1,855	778
Less: Preferred stock dividends	11			0					34	0
Net income (loss) available to Holdings’ common shareholders	$ (790)			$ (374)					$ 556	$ (818)			$ 778
Net income (loss) attributable to Holdings per common share:
Basic (in usd per share)	$ (1.77)	$ (8.94)	$ 11.66	$ (0.76)	$ 0.74	$ (1.55)	$ 2.95	$ (0.88)	$ 1.23	$ (1.64)	$ (3.57)	$ 3.33	$ 1.39
Diluted (in usd per share)	$ (1.77)	$ (8.94)	$ 11.60	$ (0.76)	$ 0.73	$ (1.55)	$ 2.94	$ (0.88)	$ 1.22	$ (1.64)	$ (3.57)	$ 3.33	$ 1.39
Effect of dilutive securities (in shares)	1.5			1.0						0.8