Other Income and Expense (Nonoperating Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total other income	$ 120		$ 64	$ 84
Other Income [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Litigation Settlement, Amount Awarded from Other Party	60	[1]	0	0
Public Utilities, Allowance for Funds Used During Construction, Additions	26		29	17
Gain (Loss) on Disposition of Other Assets	1		4	17
Gain (Loss) on Contract Termination	0		0	20
Other	33		31	30
Total other income	$ 120		$ 64	$ 84

[1] In December 2016, the Company and YPF entered into a settlement 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.