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Income Taxes Unrecognized Benefits (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Unrecognized tax benefit — Permanent tax positions	$ 46,000,000	$ 41,000,000
Unrecognized tax benefit — Temporary tax positions	11,000,000	11,000,000
Total unrecognized tax benefit	57,000,000	52,000,000
NOL and tax credit carryforwards	35,000,000	31,000,000
Decrease in Unrecognized Tax Benefits is Reasonably Possible	27,000,000
Potential Tax Adjustments	0
Unrecognized Tax Benefits, Income Tax Penalties Accrued	0	0
Unrecognized Tax Benefits, Interest on Income Taxes Accrued	(3,000,000)	(3,000,000)	$ 0
Unrecognized Tax Benefits, Interest on Income Taxes Expense	$ 0	$ (3,000,000)

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- Definition

Amount of decrease reasonably possible in the next twelve months for the unrecognized tax benefit.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (d)(3)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32718-109319

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Amount of unrecognized tax benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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-SubTopic 10
-Section 45
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Amount of statutory penalties accrued for a tax position claimed or expected to be claimed by the entity, in its tax return.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
-Paragraph 15
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Amount of interest expense accrued for an underpayment of income taxes.

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Amount of interest expense for an underpayment of income taxes.

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The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate.

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The potential income tax expense that could become payable in the event of a successful challenge by a taxing authority of an entity's income tax position.

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Tax benefits associated with NOL and tax credit carryforwards that reduce unrecognized tax benefits.

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The total amount of unrecognized tax benefits for which the ultimate deductibility is highly certain but for which there is uncertainty about the timing of such deductibility and, if recognized, would not affect the effective tax rate but would accelerate the payment of cash to the taxing authority to an earlier period.

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