Recently Issued Accounting Standards - Impact of the Adoption of the New Lease Standard on the Statement of Cash Flows (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash Flows from Operating Activities:
Net cash provided by operating activities	$ 5,728	$ 5,035	[1]
Cash Flows from Investing Activities:
Capital expenditures	(3,336)	(2,496)	[1]
Cash Flows from Financing Activities:
Proceeds from issuance of long-term debt	1,109	1,241	[1]
Principal payments under finance leases	$ (105)	(57)	[1]
As Reported
Cash Flows from Operating Activities:
Net cash provided by operating activities		5,080
Cash Flows from Investing Activities:
Capital expenditures		(2,592)
Cash Flows from Financing Activities:
Proceeds from issuance of long-term debt		1,332
Principal payments under finance leases		(98)
New Lease Standard | Adjustments
Cash Flows from Operating Activities:
Net cash provided by operating activities		(45)
Cash Flows from Investing Activities:
Capital expenditures		96
Cash Flows from Financing Activities:
Proceeds from issuance of long-term debt		(91)
Principal payments under finance leases		$ 41

[1] Amounts adjusted due to the adoption of Accounting Standards Update No. 2016-02, Leases (Topic 842). See Note 1 to the financial statements contained in Part I, Item 1 of this report for additional information.