Balance Sheet Components Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Current	$ 21	$ 61
Regulatory assets - noncurrent	380	401
Regulatory Liability, Current	41	36
Regulatory liabilities-noncurrent	1,356	1,355
Removal Costs [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liability, Current	0	0
Regulatory liabilities-noncurrent	991	979
Deferred Income Tax Charge [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities-noncurrent	266	267
Environmental Restoration Costs [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liability, Current	2	1
Regulatory liabilities-noncurrent	0	0
Asset Retirement Obligation Costs [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liability, Current	0	0
Regulatory liabilities-noncurrent	53	53
Revenue Subject to Refund [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liability, Current	23	23
Regulatory liabilities-noncurrent	16	22
Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Liability, Current	16	12
Regulatory liabilities-noncurrent	30	34
Deferred Derivative Gain (Loss) [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Current	0	32
Regulatory assets - noncurrent	74	99
Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Current	0	0
Regulatory assets - noncurrent	219	222
Loss on Reacquired Debt [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Current	0	0
Regulatory assets - noncurrent	20	16
Environmental Restoration Costs [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Current	0	0
Regulatory assets - noncurrent	25	26
Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets and Liabilities [Line Items]
Regulatory Assets, Current	21	29
Regulatory assets - noncurrent	$ 42	$ 38