Recently Issued Accounting Standards - Impact of the Adoption of the New Lease Standard on the Statement of Cash Flows (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Cash Flows from Operating Activities:
Net cash provided by operating activities	$ 4,625	$ 4,152	[1]
Cash Flows from Investing Activities:
Capital expenditures	(2,467)	(1,671)	[1]
Cash Flows from Financing Activities:
Proceeds from issuance of long-term debt	996	1,241	[1]
Principal payments under finance leases	$ (63)	(35)	[1]
As Reported
Cash Flows from Operating Activities:
Net cash provided by operating activities		4,175
Cash Flows from Investing Activities:
Capital expenditures		(1,734)
Cash Flows from Financing Activities:
Proceeds from issuance of long-term debt		1,308
Principal payments under finance leases		(62)
New Lease Standard | Adjustments
Cash Flows from Operating Activities:
Net cash provided by operating activities		(23)
Cash Flows from Investing Activities:
Capital expenditures		63
Cash Flows from Financing Activities:
Proceeds from issuance of long-term debt		(67)
Principal payments under finance leases		$ 27

[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.