RETIREMENT BENEFITS Retirement Benefits - Fair Value of Assets by Category (Details) - USD ($) $ in Millions		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan, Plan Assets, Amount		$ 191	$ 169
Cash and Cash Equivalents
Defined Benefit Plan, Plan Assets, Amount		11	9
Market index fund [Member]
Defined Benefit Plan, Plan Assets, Amount	[1]	87	73
International index fund [Member]
Defined Benefit Plan, Plan Assets, Amount	[2]	18	17
U.S. bond index fund [Member]
Defined Benefit Plan, Plan Assets, Amount	[3]	75	70
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan, Plan Assets, Amount		$ 191	$ 169	$ 141
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			1.00%
International Securities Funds			99.00%
Other Postretirement Benefits Plan [Member] | U.S. bond index fund [Member]
Large Cap US Equitiies			26.00%
Fixed Income Securities			41.00%

[1] The fund invests primarily in common stocks included in the Dow Jones U.S. Total Stock Market Index. As of December 31, 2020, this fund was invested 100% in domestic equities.

[2] The fund invests primarily in both the securities and in depository receipts representing securities included in the MSCI All Country World Index. As of December 31, 2020, this fund was invested 99% in foreign equities and 1% in domestic equities.

[3] The fund invests primarily in bonds included in the Bloomberg Barclays U.S. Aggregate Bond Index. As of December 31, 2020, this fund was invested 41% in U.S. Treasury, 25% in mortgage-backed securities, 26% in corporations and 8% in other.