Regulatory Assets and Liabilities, Regulatory Assets (Details) - USD ($) $ in Millions		Dec. 31, 2019	Dec. 31, 2018
Regulatory Assets [Line Items]
Regulatory Asset, Current		$ 488	$ 464
Regulatory Asset, Noncurrent		2,935	3,326
Pension and retiree medical obligations
Regulatory Assets [Line Items]
Regulatory Asset, Current		85	87
Regulatory Asset, Noncurrent		1,328	1,500
Recoverable deferred taxes on AFUDC recorded in plant
Regulatory Assets [Line Items]
Regulatory Asset, Current		0	0
Regulatory Asset, Noncurrent		271	264
Net AROs
Regulatory Assets [Line Items]
Regulatory Asset, Current	[1]	0	0
Regulatory Asset, Noncurrent	[1]	269	452
Excess deferred taxes - TCJA
Regulatory Assets [Line Items]
Regulatory Asset, Current		39	0
Regulatory Asset, Noncurrent		239	296
Depreciation differences
Regulatory Assets [Line Items]
Regulatory Asset, Current		15	18
Regulatory Asset, Noncurrent		140	107
Environmental remediation costs
Regulatory Assets [Line Items]
Regulatory Asset, Current		36	17
Regulatory Asset, Noncurrent		131	155
Benson Biomass PPA termination and asset purchase
Regulatory Assets [Line Items]
Regulatory Asset, Current		9	10
Regulatory Asset, Noncurrent		73	86
Contract valuation adjustments
Regulatory Assets [Line Items]
Regulatory Asset, Current	[2]	20	17
Regulatory Asset, Noncurrent	[2]	62	77
Purchased power contract costs
Regulatory Assets [Line Items]
Regulatory Asset, Current		5	4
Regulatory Asset, Noncurrent		61	63
Laurentian biomass PPA termination
Regulatory Assets [Line Items]
Regulatory Asset, Current		19	18
Regulatory Asset, Noncurrent		54	73
PI extended power update
Regulatory Assets [Line Items]
Regulatory Asset, Current		3	3
Regulatory Asset, Noncurrent		53	56
Losses on reacquired debt
Regulatory Assets [Line Items]
Regulatory Asset, Current		4	4
Regulatory Asset, Noncurrent		41	44
State commission adjustments
Regulatory Assets [Line Items]
Regulatory Asset, Current		1	1
Regulatory Asset, Noncurrent		31	29
Property tax
Regulatory Assets [Line Items]
Regulatory Asset, Current		2	14
Regulatory Asset, Noncurrent		30	10
Conservation programs
Regulatory Assets [Line Items]
Regulatory Asset, Current	[3]	27	42
Regulatory Asset, Noncurrent	[3]	26	28
Nuclear refueling outage costs
Regulatory Assets [Line Items]
Regulatory Asset, Current		43	37
Regulatory Asset, Noncurrent		17	14
Sales true-up and revenue decoupling
Regulatory Assets [Line Items]
Regulatory Asset, Current		54	38
Regulatory Asset, Noncurrent		16	7
Renewable resources and environmental initiatives
Regulatory Assets [Line Items]
Regulatory Asset, Current		72	39
Regulatory Asset, Noncurrent		10	9
Gas pipeline inspection and remediation costs
Regulatory Assets [Line Items]
Regulatory Asset, Current		26	28
Regulatory Asset, Noncurrent		8	3
Deferred purchased natural gas and electric energy costs
Regulatory Assets [Line Items]
Regulatory Asset, Current		6	57
Regulatory Asset, Noncurrent		6	13
Other
Regulatory Assets [Line Items]
Regulatory Asset, Current		22	30
Regulatory Asset, Noncurrent		$ 69	$ 40

[1] Includes amounts recorded for future recovery of AROs, less amounts recovered through nuclear decommissioning accruals and gains from decommissioning investments.

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

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