Income Taxes - Narrative (Details) - USD ($) $ in Millions	2 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017
Operating Loss Carryforwards [Line Items]
Statutory federal rate percentage	21.00%	35.00%
Deferred tax asset related to net operating loss carryforward	$ 990
Federal Net Operating Loss Carryforwards And Other Deferred Tax Assets
Operating Loss Carryforwards [Line Items]
Decrease in valuation allowance	$ 990

Amount before allocation of valuation allowances of deferred tax asset attributable to deductible operating loss carryforwards.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Amount of increase (decrease) in the valuation allowance for a specified deferred tax asset.

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