Commitments and Contingencies - Environmental Matters (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Jun. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Environmental remediation accrual, discounted basis	$ 40
Portion of environmental remediation costs recorded in other current liabilities	12
Portion of environmental remediation costs recorded in deferred credits and other liabilities	$ 28
Weighted average discount rate	2.90%
Environmental remediation accrual, undiscounted basis	$ 46
Expected payments of environmental remediation costs, 2019	10
Expected payments of environmental remediation costs, 2020	6
Expected payments of environmental remediation costs, 2021	3
Expected payments of environmental remediation costs, 2022	3
Expected payments of environmental remediation costs, 2023	2
Expected payments of environmental remediation costs, thereafter	16
Future Property, Plant And Equipment, Estimated Environmental Costs, Next Twelve Months	14
Future Property, Plant And Equipment, Estimated Environmental Costs, Year Two	7
Estimated liability	53	$ 132
Payments for settlement	$ 79