RETIREMENT BENEFITS Retirement Benefits - Fair Value of Assets by Category (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan, Plan Assets, Amount	$ 141	$ 143
Cash and Cash Equivalents
Defined Benefit Plan, Plan Assets, Amount	14	12
Target 2020 Fund [Member]
Defined Benefit Plan, Plan Assets, Amount	0	123
Target 2050 Fund [Member]
Defined Benefit Plan, Plan Assets, Amount	0	8
Market index fund [Member]
Defined Benefit Plan, Plan Assets, Amount	53	0
International index fund [Member]
Defined Benefit Plan, Plan Assets, Amount	13	0
U.S. bond index fund [Member]
Defined Benefit Plan, Plan Assets, Amount	61	0
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan, Plan Assets, Amount	$ 141	$ 143	$ 126
Other Postretirement Benefits Plan [Member] | Target 2020 Fund [Member]
Large Cap US Equitiies		32.00%
Fixed Income Securities		52.00%
International Securities Funds		16.00%
Other Postretirement Benefits Plan [Member] | Target 2050 Fund [Member]
Large Cap US Equitiies		54.00%
Fixed Income Securities		10.00%
Cash Fund Investments		36.00%
Other Postretirement Benefits Plan [Member] | Market index fund [Member]
Large Cap US Equitiies		100.00%
Other Postretirement Benefits Plan [Member] | International index fund [Member]
Large Cap US Equitiies		4.00%
International Securities Funds		96.00%
Other Postretirement Benefits Plan [Member] | U.S. bond index fund [Member]
Large Cap US Equitiies		23.00%
Fixed Income Securities		41.00%