Regulatory Assets and Liabilities, Regulatory Liabilities (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	[1]	$ 436	$ 239
Regulatory Liability, Noncurrent	[1]	5,187	5,083
Deferred Income Tax Adjustment and TCJA Refunds
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	[2]	157	0
Regulatory Liability, Noncurrent	[2]	$ 3,715	3,790
Regulatory liability, remaining amortization period		Various
Plant Removal Costs
Regulatory Liabilities [Line Items]
Regulatory Liability, Current		$ 0	0
Regulatory Liability, Noncurrent		$ 1,175	1,131
Regulatory liability, remaining amortization period		Plant lives
Effects of regulation on employee benefit costs
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	[3]	$ 0	0
Regulatory Liability, Noncurrent	[3]	$ 137	46
Regulatory liability, remaining amortization period		Various
Renewable Resources and Environmental Initiatives
Regulatory Liabilities [Line Items]
Regulatory Liability, Current		$ 9	19
Regulatory Liability, Noncurrent		$ 54	60
Regulatory liability, remaining amortization period		Various
Investment Tax Credit Deferrals
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	[4]	$ 0	0
Regulatory Liability, Noncurrent	[4]	$ 40	23
Regulatory liability, remaining amortization period		Various
Deferred Electric, Natural Gas and Steam Production Costs
Regulatory Liabilities [Line Items]
Regulatory Liability, Current		$ 102	104
Regulatory Liability, Noncurrent		$ 0	0
Regulatory liability remaining amortization period, maximum		1 year
Contract Valuation Adjustments
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	[5]	$ 26	30
Regulatory Liability, Noncurrent	[5]	$ 0	0
Regulatory liability remaining amortization period, maximum		1 year
Conservation Programs
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	[6]	$ 36	23
Regulatory Liability, Noncurrent	[6]	$ 0	0
Regulatory liability remaining amortization period, maximum		1 year
DOE Settlement
Regulatory Liabilities [Line Items]
Regulatory Liability, Current		$ 19	18
Regulatory Liability, Noncurrent		$ 0	0
Regulatory liability remaining amortization period, maximum		1 year
Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Regulatory Liability, Current		$ 87	45
Regulatory Liability, Noncurrent		$ 66	33
Regulatory liability, remaining amortization period		Various
Other Current Liabilities
Regulatory Liabilities [Line Items]
Entity's Recorded Provision for Revenue Subject To Refund		$ 29	$ 15

[1] Revenue subject to refund of $29 million and $15 million for 2018 and 2017, respectively, is included in other current liabilities.

[2] Includes the revaluation of recoverable/regulated plant ADIT and revaluation impact of non-plant ADIT due to the TCJA.

[3] Includes regulatory amortization and certain TCJA benefits approved by the CPUC to offset the PSCo prepaid pension asset at Dec. 31, 2018.

[4] Includes impact of lower federal tax rate due to the TCJA.

[5] Includes the fair value of certain long-term PPAs used to meet energy capacity requirements and valuation adjustments on natural gas commodity purchases.

[6] Includes costs for conservation programs, as well as incentives allowed in certain jurisdictions.