Income Taxes - Future Tax Benefits (Details) $ in Millions	Sep. 30, 2018 USD ($)
Foreign tax credit carryover
Tax Credit Carryforward [Line Items]
Tax credit carryover, Carryover amount	$ 5
Foreign tax credit credit carryover, Expected tax benefit, gross	5
Foreign tax credit carryover \| Expiring within Tax Years 2023 to 2024
Tax Credit Carryforward [Line Items]
Tax credit carryover, Carryover amount	5
General business credit carryover
Tax Credit Carryforward [Line Items]
Tax credit carryover, Carryover amount	4
General business credit carryover, Expected tax benefit, gross	4
General business credit carryover \| Expiring Tax Year 2031 to 2037
Tax Credit Carryforward [Line Items]
Tax credit carryover, Carryover amount	4
U.S.
Tax Credit Carryforward [Line Items]
Operating Loss Carryforwards	2,814
Net operating loss carryover, Expected tax benefit, gross	591
U.S. \| Expiring Tax Year 2020
Tax Credit Carryforward [Line Items]
Operating Loss Carryforwards	2,814
Foreign
Tax Credit Carryforward [Line Items]
Operating Loss Carryforwards	4
Net operating loss carryover, Expected tax benefit, gross	0
Foreign \| No expiration tax year
Tax Credit Carryforward [Line Items]
Operating Loss Carryforwards	$ 4

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

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