Financial Instruments - Long-Term Debt (Details) - USD ($) $ in Millions		Jun. 30, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Net fair value adjustments related to hedging and purchase accounting		$ 0	$ (5)
Net unamortized discounts, premiums and debt issuance costs		(29)	(11)
Total long-term debt, carried at historical proceeds, as adjusted	[1]	36,168	32,909
Current portion of long-term debt, carried at historical proceeds, as adjusted	[1]	2,139	4,776
Unsecured Debt [Member]
Debt Instrument [Line Items]
Total long-term debt, principal amount		35,082	32,558
Net fair value adjustments related to hedging and purchase accounting		1,264	479
Net unamortized discounts, premiums and debt issuance costs		(185)	(136)
Other long-term debt		6	7
Total long-term debt, carried at historical proceeds, as adjusted		36,168	32,909
Current portion of long-term debt, carried at historical proceeds, as adjusted		$ 2,139	$ 4,776

[1] Amounts may not add due to rounding.