Income Taxes (Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Valuation Allowance [Line Items]
Income Tax Expense (Benefit), Intraperiod Tax Allocation	$ 0	$ 1	$ 6
NOL and credit carryforwards	1,731	1,595
Taxes related to risk management activities and derivatives	18	7
Reorganization items and impairments	73	166
Deferred Tax Assets, Other	62	101
Deferred tax assets before valuation allowance	1,884	1,869
Valuation allowance	(873)	(1,000)
Valuation Allowance, Deferred Tax Asset, Change in Amount	127
Total deferred tax assets	1,011	869
Deferred tax liabilities: property, plant and equipment	(1,125)	(890)
Deferred Tax Liabilities, Gross	(1,125)	(890)
Deferred Tax Liabilities, Net	114
Deferred Tax Assets, Net		21
Deferred Tax Liabilities, Gross, Noncurrent	(116)	(22)
Deferred Tax Assets, Gross, Noncurrent	$ 2	1
Change in Valuation due to Merger [Member]
Valuation Allowance [Line Items]
Valuation Allowance, Deferred Tax Asset, Change in Amount		$ (58)