Fair Value Measurements and Guarantees Recurring Measurements and Additional (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Carrying Amount [Member]
Additional disclosures:
Long-term debt, including current portion	$ (22,343)	$ (22,288)
Guarantees	(41)	(41)
Fair Value [Member]
Additional disclosures:
Long-term debt, including current portion	(26,000)	(25,319)
Guarantees	(27)	(27)
Level 1 [Member]
Additional disclosures:
Long-term debt, including current portion	0	0
Guarantees	0	0
Level 2 [Member]
Additional disclosures:
Long-term debt, including current portion	(26,000)	(25,319)
Guarantees	(11)	(11)
Level 3 [Member]
Additional disclosures:
Long-term debt, including current portion	0	0
Guarantees	(16)	(16)
Fair Value, Recurring [Member] \| Carrying Amount [Member]
Measured on a recurring basis:
ARO Trust investments	220	201
Fair Value, Recurring [Member] \| Fair Value [Member]
Measured on a recurring basis:
ARO Trust investments	220	201
Fair Value, Recurring [Member] \| Level 1 [Member]
Measured on a recurring basis:
ARO Trust investments	220	201
Fair Value, Recurring [Member] \| Level 2 [Member]
Measured on a recurring basis:
ARO Trust investments	0	0
Fair Value, Recurring [Member] \| Level 3 [Member]
Measured on a recurring basis:
ARO Trust investments	0	$ 0
WilTel Guarantee [Member]
Additional disclosures:
Guarantor Obligations, Maximum Exposure, Undiscounted	27
Indemnification Agreement [Member] \| Carrying Amount [Member]
Additional disclosures:
Guarantees	$ 0

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- Definition

Carrying amount of an asset that is legally restricted for purposes of settling an asset retirement obligation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

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- References

No definition available.

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- Definition

Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
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- Definition

Fair value portion of guarantee, including, but not limited to, financial standby letter of credit, fair value guarantee, guarantee of collection of scheduled contractual cash flows from financial assets, and contracts that contingently require the guarantor to make payments or perform services.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121555522&loc=d3e12201-110248

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- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

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