INCOME TAXES - Effective Income Tax Rate Applicable (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Expense Benefit Continuing Operations Income Tax Reconciliation [Abstract]
U.S. federal statutory income tax		$ (45)	$ 170	$ 250
State income taxes, net of federal tax benefit		(31)	8	(2)
REIT income not subject to federal income tax		(68)	(116)	(198)
SDT settlement	$ 21	0	21	0
Tax effect of U.S. corporate rate change		0	0	74
Voluntary pension contribution		0	(41)	0
Return to provision adjustment		4	(1)	2
Foreign taxes		(2)	15	54
Repatriation of Canadian earnings		0	0	(22)
Other, net		5	3	(24)
Total income tax provision (benefit)		$ (137)	$ 59	$ 134
Effective income tax rate		64.10%	7.30%	18.80%