Summary of Significant Accounting Policies - Income tax (Details) - Adjustment Effect - West Virginia $ in Millions	Sep. 30, 2021 USD ($)
Income taxes
Deferred tax liabilities	$ (34)
Deferred tax assets	48
Valuation allowance	$ 14

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards.

+ References

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-Publisher FASB
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Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.

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Amount, after deferred tax asset, of deferred tax liability attributable to taxable differences without jurisdictional netting.

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