Regulatory Assets and Liabilities, Regulatory Assets (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019
Regulatory Assets [Line Items]
Regulatory Asset, Current		$ 121	$ 64
Regulatory Asset, Noncurrent		1,059	1,038
Regulatory assets not currently earning a return		195	160
Pension and Retiree Medical Obligations
Regulatory Assets [Line Items]
Regulatory Asset, Current		28	23
Regulatory Asset, Noncurrent		478	494
Depreciation differences
Regulatory Assets [Line Items]
Regulatory Asset, Current		16	15
Regulatory Asset, Noncurrent		$ 154	140
Depreciation differences | Minimum
Regulatory Assets [Line Items]
Regulatory Asset, Amortization Period		1 year
Depreciation differences | Maximum
Regulatory Assets [Line Items]
Regulatory Asset, Amortization Period		11 years
Net AROs
Regulatory Assets [Line Items]
Regulatory Asset, Current	[1]	$ 0	0
Regulatory Asset, Noncurrent	[1]	132	119
Recoverable Deferred Taxes on AFUDC Recorded in Plant
Regulatory Assets [Line Items]
Regulatory Asset, Current		0	0
Regulatory Asset, Noncurrent		110	105
Excess deferred taxes - TCJA
Regulatory Assets [Line Items]
Regulatory Asset, Current		3	3
Regulatory Asset, Noncurrent		56	55
Purchased Power Agreements
Regulatory Assets [Line Items]
Regulatory Asset, Current		3	2
Regulatory Asset, Noncurrent		22	24
Property Tax
Regulatory Assets [Line Items]
Regulatory Asset, Current		16	1
Regulatory Asset, Noncurrent		21	30
Conservation programs
Regulatory Assets [Line Items]
Regulatory Asset, Current	[2]	11	8
Regulatory Asset, Noncurrent	[2]	$ 11	11
Conservation programs | Minimum
Regulatory Assets [Line Items]
Regulatory Asset, Amortization Period		1 year
Conservation programs | Maximum
Regulatory Assets [Line Items]
Regulatory Asset, Amortization Period		2 years
Gas pipeline inspection costs
Regulatory Assets [Line Items]
Regulatory Asset, Current		$ 0	0
Regulatory Asset, Noncurrent		$ 9	8
Gas pipeline inspection costs | Minimum
Regulatory Assets [Line Items]
Regulatory Asset, Amortization Period		1 year
Gas pipeline inspection costs | Maximum
Regulatory Assets [Line Items]
Regulatory Asset, Amortization Period		2 years
Losses on Reacquired Debt
Regulatory Assets [Line Items]
Regulatory Asset, Current		$ 1	1
Regulatory Asset, Noncurrent		3	4
Contract Valuation Adjustments
Regulatory Assets [Line Items]
Regulatory Asset, Current	[3]	6	3
Regulatory Asset, Noncurrent	[3]	0	0
Recoverable Purchased Natural Gas and Electric Energy Costs
Regulatory Assets [Line Items]
Regulatory Asset, Current		6	0
Regulatory Asset, Noncurrent		0	0
Other
Regulatory Assets [Line Items]
Regulatory Asset, Current		31	8
Regulatory Asset, Noncurrent		$ 63	$ 48

[1] Includes amounts recorded for future recovery of AROs.

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

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