BENEFITS Benefits - Fair Value of Assets by Category (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan, Fair Value of Plan Assets	$ 143	$ 126
Cash and Cash Equivalents
Defined Benefit Plan, Fair Value of Plan Assets	12	8
Fixed Income Funds [Member]
Defined Benefit Plan, Fair Value of Plan Assets	123	112
Balanced Funds [Member]
Defined Benefit Plan, Fair Value of Plan Assets	$ 8	6
Other Postretirement Benefits Plan [Member]
Large Cap US Equitiies	32.00%
International Securities Funds	16.00%
Defined Benefit Plan, Fair Value of Plan Assets	$ 143	$ 126	$ 118
Fixed Income Securities	52.00%
Other Postretirement Benefits Plan [Member] | Balanced Funds [Member]
Large Cap US Equitiies	54.00%
Fixed Income Securities	10.00%
Cash Fund Investments	36.00%