Consolidated Statements of Comprehensive Loss - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement [Abstract]
Operating Revenue	[1]	$ 1,929	$ 2,762	$ 3,070
Operating Expenses:
Fuel used in electric generation	[1]	573	671	594
Purchased power	[1]	54	92	80
Gas purchased for resale	[1]	216	239	206
Other operations and maintenance		388	449	417
Other operations and maintenance – affiliated suppliers		244	182	180
Impairment of assets and other charges		695	1,376	1,118
Depreciation and amortization		450	327	312
Other taxes	[1]	250	257	246
Total operating expenses		2,870	3,593	3,153
Operating loss		(941)	(831)	(83)
Other income (expense), net		(33)	129	28
Interest charges, net of allowance for funds used during construction	[1]	260	303	288
Loss before income tax benefit		(1,234)	(1,005)	(343)
Income tax benefit		(12)	(416)	(171)
Net Loss		(1,222)	(589)	(172)
Other Comprehensive Income:
Deferred cost of employee benefit plans, net of tax		1	1	0
Total Comprehensive Loss		(1,221)	(588)	(172)
Comprehensive Income Attributable to Noncontrolling Interest		18	25	13
Comprehensive Loss Attributable to Common Shareholder		$ (1,239)	$ (613)	$ (185)

[1] See Note 16 for amounts attributable to affiliates.