Other Income and Expense - Other Income (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Schedule of Other Nonoperating Income [Line Items]
Other income		$ 10	$ 16	$ 30	$ 103
Other Income [Member]
Schedule of Other Nonoperating Income [Line Items]
Litigation Settlement, Amount Awarded from Other Party	[1]	0	0	0	60
Public Utilities, Allowance for Funds Used During Construction, Additions		1	7	8	20
Other Nonoperating Income		9	9	22	23
Other income		$ 10	$ 16	$ 30	$ 103

[1] (1) In December 2016, the Company and YPF entered into a settlement agreement in which all parties agreed to give up any and all legal action related to gas supply contracts that were terminated in 2008 and have been in dispute since 2009. In January 2017, the YPF board approved the agreement and paid the Company $60 million, thereby resolving all uncertainties around the dispute.