Financial Instruments - Investments - Unrealized Gains and Losses Related to Equity Securities - Footnotes (Details) - USD ($) $ in Millions		3 Months Ended	9 Months Ended
		Sep. 30, 2018	Sep. 30, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net unrealized gains during the reporting period on equity securities still held at the reporting date	[1]	$ 40	$ 370
Financial Assets and Liabilities [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net unrealized gains during the reporting period on equity securities still held at the reporting date		8	344
Other equity securities [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net unrealized gains during the reporting period on equity securities still held at the reporting date		$ 32	$ 26

[1] The third quarter of 2018 includes $8 million of unrealized net gains in Other (income)/deductions––net reflecting the adoption of a new accounting standard in the first quarter of 2018 and $32 million of unrealized gains on other equity securities. The first nine months of 2018 includes $344 million of unrealized net gains in Other (income)/deductions––net reflecting the adoption of a new accounting standard in the first quarter of 2018 and $26 million of unrealized gains on other equity securities. For additional information, see Note 1B and Note 4.