Income Taxes - Future Tax Benefits (Details) $ in Millions	Mar. 31, 2018 USD ($)
Foreign tax credit carryover | Expiring within Tax Years 2023 to 2024
Tax Credit Carryforward [Line Items]
Tax credit carryover, Carryover amount	$ 21
Foreign tax credit credit carryover, Expected tax benefit, gross	21
General business credit carryover
Tax Credit Carryforward [Line Items]
Tax credit carryover, Carryover amount	3
General business credit carryover, Expected tax benefit, gross	3
General business credit carryover | Expiring Tax Year 2031 to 2037
Tax Credit Carryforward [Line Items]
General business credit carryover, Expected tax benefit, gross	3
U.S.
Tax Credit Carryforward [Line Items]
Operating Loss Carryforwards	3,087
Net operating loss carryover, Expected tax benefit, gross	648
U.S. | Expiring Tax Year 2020
Tax Credit Carryforward [Line Items]
Operating Loss Carryforwards	1
U.S. | Expiring within Tax Years 2023 to 2036
Tax Credit Carryforward [Line Items]
Operating Loss Carryforwards	3,086
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