Balance Sheet Components Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Current	$ 26	$ 61
Regulatory assets - noncurrent	483	401
Regulatory Liability, Current	40	36
Regulatory liabilities-noncurrent	1,380	1,355
Removal Costs [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liability, Current	0	0
Regulatory liabilities-noncurrent	1,011	979
Deferred Income Tax Charge [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liability, Current	0	0
Regulatory liabilities-noncurrent	262	267
Asset Retirement Obligation Costs [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liability, Current	0	0
Regulatory liabilities-noncurrent	54	53
Revenue Subject to Refund [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liability, Current	23	23
Regulatory liabilities-noncurrent	6	22
Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liability, Current	17	13
Regulatory liabilities-noncurrent	47	34
Deferred Derivative Gain (Loss) [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Current	12	32
Regulatory assets - noncurrent	96	99
Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Current	0	0
Regulatory assets - noncurrent	218	222
Loss on Reacquired Debt [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Current	0	0
Regulatory assets - noncurrent	18	16
Environmental Restoration Costs [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Current	0	0
Regulatory assets - noncurrent	93	26
Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Current	14	29
Regulatory assets - noncurrent	$ 58	$ 38