INCOME TAXES - Effective Income Tax Rate Applicable to Continuing Operations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
U.S. federal statutory income tax	$ 170	$ 250	$ 177
State income taxes, net of federal tax benefit	8	(2)	(3)
REIT income not subject to federal income tax	(116)	(198)	(99)
SDT settlement	21	0	0
Tax affect of U.S. corporate rate change	0	74	0
Voluntary pension contribution	(41)	0	0
Foreign taxes	15	54	(4)
Repatriation of Canadian earnings	0	(22)	24
Other, net	2	(22)	(6)
Total income tax provision (benefit)	$ 59	$ 134	$ 89
Effective income tax rate	7.30%	18.80%	17.60%