Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Taxes [Line Items]
Effective tax rate	0.00%	0.00%	0.00%	(16.00%)
Valuation allowance related to operating loss	$ 87		$ 87
Federal
Income Taxes [Line Items]
Operating loss carryforwards subject to a section 382 limitation	2,000		2,000
Operating loss carryforwards	4,500		4,500
Deferred tax assets, operating loss carryforwards, subject to expiration	3,000		3,000
Deferred tax assets, operating loss carryforwards, not subject to expiration	1,500		1,500
Indigo Natural Resources, LLC
Income Taxes [Line Items]
Operating loss carryforwards subject to a section 382 limitation	$ 48		$ 48

Income Taxes

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- Definition

Operating Loss Carryforwards, Limitation of Use

+ References

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible operating loss carryforwards that are not subject to expiration dates.

+ References

No definition available.

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- Definition

Amount before allocation of valuation allowances of deferred tax asset attributable to deductible operating loss carryforwards that are subject to expiration dates.

+ References

No definition available.

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- Definition

Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32687-109319

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- Definition

Amount of operating loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws.

+ References

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-Publisher FASB
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-Topic 740
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The portion of the valuation allowance pertaining to the deferred tax asset representing potential future taxable deductions from net operating loss carryforwards for which it is more likely than not that a tax benefit will not be realized.

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