Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
Schedule of Regulatory Assets and Liabilities [Line Items]
Total Current Regulatory Assets		$ 156	$ 119
Total Non Current Regulatory Assets		$ 547	542
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided		8 years
TOTAL REGULATORY ASSETS		$ 703	661
Total Current Regulatory Liabilities		$ 86	17
Remaining Recovery Period of Regulatory Liabilities		1 year
Total Non Current Regulatory Liabilities		$ 1,146	1,079
TOTAL REGULATORY LIABILITIES		1,232	1,096
Overcollection of Costs [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total Current Regulatory Liabilities		83	14
Deferred Income Tax Charge [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total Non Current Regulatory Liabilities		246	243
Asset Retirement Obligation Costs
Schedule of Regulatory Assets and Liabilities [Line Items]
Total Non Current Regulatory Liabilities		847	830
Other Regulatory Liabilities
Schedule of Regulatory Assets and Liabilities [Line Items]
Total Current Regulatory Liabilities		3	3
Total Non Current Regulatory Liabilities		53	6
El Salvador Tariff Recoveries
Schedule of Regulatory Assets and Liabilities [Line Items]
Total Current Regulatory Assets		87	59
Pension Costs
Schedule of Regulatory Assets and Liabilities [Line Items]
Total Non Current Regulatory Assets	[1]	283	298
Deferred Midwest Independent Service Operator Costs
Schedule of Regulatory Assets and Liabilities [Line Items]
Total Non Current Regulatory Assets		88	102
Environmental Restoration Costs [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Total Non Current Regulatory Assets		89	48
Other Regulatory Assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Total Current Regulatory Assets		69	60
Total Non Current Regulatory Assets		$ 87	$ 94

[1] Past expenditures on which the Company earns a rate of return.