Regulatory Assets and Liabilities (Tables)

12 Months Ended

Dec. 31, 2018

Regulatory Assets and Liabilities Disclosure [Abstract]

Regulatory Assets

Components of regulatory assets:

(Millions of Dollars)	See Note(s)	Remaining Amortization Period	Dec. 31, 2018				Dec. 31, 2017
Regulatory Assets			Current		Non- current		Current		Non- current
Pension and retiree medical obligations	11	Various	$	87	$	1,500	$	91	$	1,499
Net AROs (a)	1, 12	Plant lives	—		452		—		301
Excess deferred taxes - TCJA	7	Various	—		296		—		254
Recoverable deferred taxes on AFUDC recorded in plant		Plant lives	—		264		—		244
Environmental remediation costs	1, 12	Various	17		155		16		165
Depreciation differences		One to thirteen years	18		107		20		69
Benson biomass PPA termination and asset purchase		Ten years	10		86		—		—
Contract valuation adjustments (b)	1, 10	Term of related contract	17		77		21		93
Laurentian biomass PPA termination		Five years	18		73		—		—
Purchased power contract costs		Term of related contract	4		63		3		67
PI EPU		Sixteen years	3		56		3		58
Losses on reacquired debt		Term of related debt	4		44		5		48
State commission adjustments		Plant lives	1		29		1		29
Conservation programs (c)	1	One to two years	42		28		50		32
Property tax		Various	14		10		8		24
Nuclear refueling outage costs	1	One to two years	37		14		49		20
Deferred purchased natural gas and electric energy costs		One to three years	57		13		21		13
Renewable resources and environmental initiatives		One to two years	39		9		48		10
Sales true up and revenue decoupling		One to two years	38		7		37		12
Gas pipeline inspection and remediation costs		One to two years	28		3		24		12
Other		Various	30		40		27		55
Total regulatory assets			$	464	$	3,326	$	424	$	3,005

^(a) Includes amounts recorded for future recovery of AROs, less amounts recovered through nuclear decommissioning accruals and gains from decommissioning investments.

^(b) Includes the fair value of certain long-term PPAs used to meet energy capacity requirements and valuation adjustments on natural gas commodity purchases.

^(c) Includes costs for conservation programs, as well as incentives allowed in certain jurisdictions.

Regulatory Liabilities

Components of regulatory liabilities:

(Millions of Dollars)	See Note(s)	Remaining Amortization Period	Dec. 31, 2018				Dec. 31, 2017
Regulatory Liabilities			Current		Non- current		Current		Non- current
Deferred income tax adjustments and TCJA refunds (a)	7	Various	$	157	$	3,715	$	—	$	3,790
Plant removal costs	1, 12	Plant lives	—		1,175		—		1,131
Effects of regulation on employee benefit costs (b)		Various	—		137		—		46
Renewable resources and environmental initiatives		Various	9		54		19		60
ITC deferrals (c)	1	Various	—		40		—		23
Deferred electric, natural gas and steam production costs		Less than one year	102		—		104		—
Contract valuation adjustments (d)	1, 10	Less than one year	26		—		30		—
Conservation programs (e)	1	Less than one year	36		—		23		—
DOE settlement		Less than one year	19		—		18		—
Other		Various	87		66		45		33
Total regulatory liabilities (f)			$	436	$	5,187	$	239	$	5,083

^(a)  Includes the revaluation of recoverable/regulated plant ADIT and revaluation impact of non-plant ADIT due to the TCJA.

^(b)  Includes regulatory amortization and certain TCJA benefits approved by the CPUC to offset the PSCo prepaid pension asset at Dec. 31, 2018.

^(c)  Includes impact of lower federal tax rate due to the TCJA.

^(d)  Includes the fair value of certain long-term PPAs used to meet energy capacity requirements and valuation adjustments on natural gas commodity purchases.

^(e)  Includes costs for conservation programs, as well as incentives allowed in certain jurisdictions.

^(f)  Revenue subject to refund of $29 million and $15 million for 2018 and 2017, respectively, is included in other current liabilities.