Consolidated Statements of Income and Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues
Electric	$ 2,063	$ 2,052	$ 1,964
Gas	461	418	432
Total revenues	2,524	2,470	2,396
Expenses
Fuel	551	588	561
Purchased power	59	46	104
Cost of natural gas sold	$ 180	$ 153	$ 159
Type of Cost, Good or Service [Extensible List]	us-gaap:OilAndGasMember	us-gaap:OilAndGasMember	us-gaap:OilAndGasMember
Operations & maintenance	$ 632	$ 513	$ 538
Depreciation and amortization	372	350	328
Taxes, other than income	208	198	193
Total expenses	2,002	1,848	1,883
Income from operations	522	622	513
Other income
Allowance for other funds used during construction	10	2	24
Other income, net	8	8	7
Total other income	18	10	31
Interest charges
Interest expense	123	120	117
Allowance for borrowed funds used during construction	(5)	(1)	(11)
Total interest charges	118	119	106
Income before provision for income taxes	422	513	438
Provision for income taxes	81	197	152
Net income	341	316	286
Other comprehensive income, net of tax
Gain on cash flow hedges	1	1	1
Total other comprehensive income, net of tax	1	1	1
Comprehensive income	$ 342	$ 317	$ 287