Regulatory Assets and Liabilities Schedule of Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Regulatory Assets [Line Items]
Regulatory Assets	$ 462	$ 500
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided	383
Regulatory Liabilities	1,391	1,319
Regulatory Assets Earning a Rate of Return at the Approved Rate	1,384
Removal Costs [Member]
Regulatory Assets [Line Items]
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided	0
Regulatory Liabilities	979	933
Deferred Income Tax Charge [Member]
Regulatory Assets [Line Items]
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided	0
Regulatory Liabilities	$ 267	277
Environmental Restoration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Current Asset, End Date for Recovery	2019
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided	$ 0
Regulatory Liabilities	1	3
Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided	0
Regulatory Liabilities	$ 53	52
Revenue Subject to Refund [Member]
Regulatory Assets [Line Items]
Regulatory Current Asset, End Date for Recovery	2020
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided	$ 0
Regulatory Liabilities	45	0
Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided	7
Regulatory Liabilities	46	54
Regulatory Assets Earning a Rate of Return at the Approved Rate	39
Other Regulatory Assets Earning a Return [Member]
Regulatory Assets [Line Items]
Regulatory Assets	53
Earning a return [Member]
Regulatory Assets [Line Items]
Regulatory Assets	$ 79
Deferred Derivative Gain (Loss) [Member]
Regulatory Assets [Line Items]
Regulatory Current Asset, End Date for Recovery	2035
Regulatory Assets	$ 0	204
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided	131
Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	218
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided	$ 222
Loss on Reacquired Debt [Member]
Regulatory Assets [Line Items]
Regulatory Current Asset, End Date for Recovery	2036
Regulatory Assets	$ 0	19
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided	$ 16
Environmental Restoration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Current Asset, End Date for Recovery	2039
Regulatory Assets	$ 26	0
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided	0
Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Regulatory Assets	67	$ 59
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided	$ 14

Regulatory assets earning a rate of return at the approved rate.

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+ References

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