Fair Value Measurements and Guarantees Recurring Measurements and Additional (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Carrying Amount [Member]
Additional disclosures:
Long-term debt, including current portion	$ (22,476)	$ (22,288)
Guarantees	(41)	(41)
Fair Value [Member]
Additional disclosures:
Long-term debt, including current portion	(22,531)	(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	(22,531)	(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	188	201
Fair Value, Recurring [Member] \| Carrying Amount [Member] \| Designated as Hedging Instrument [Member]
Measured on a recurring basis:
Energy derivative assets	2
Fair Value, Recurring [Member] \| Carrying Amount [Member] \| Not Designated as Hedging Instrument [Member]
Measured on a recurring basis:
Energy derivative assets	2	1
Energy derivative liabilities	(5)	(3)
Fair Value, Recurring [Member] \| Fair Value [Member]
Measured on a recurring basis:
ARO Trust investments	188	201
Fair Value, Recurring [Member] \| Fair Value [Member] \| Designated as Hedging Instrument [Member]
Measured on a recurring basis:
Energy derivative assets	2
Fair Value, Recurring [Member] \| Fair Value [Member] \| Not Designated as Hedging Instrument [Member]
Measured on a recurring basis:
Energy derivative assets	2	1
Energy derivative liabilities	(5)	(3)
Fair Value, Recurring [Member] \| Level 1 [Member]
Measured on a recurring basis:
ARO Trust investments	188	201
Fair Value, Recurring [Member] \| Level 1 [Member] \| Designated as Hedging Instrument [Member]
Measured on a recurring basis:
Energy derivative assets	2
Fair Value, Recurring [Member] \| Level 1 [Member] \| Not Designated as Hedging Instrument [Member]
Measured on a recurring basis:
Energy derivative assets	2	1
Energy derivative liabilities	(3)	(1)
Fair Value, Recurring [Member] \| Level 2 [Member]
Measured on a recurring basis:
ARO Trust investments	0	0
Fair Value, Recurring [Member] \| Level 2 [Member] \| Designated as Hedging Instrument [Member]
Measured on a recurring basis:
Energy derivative assets	0
Fair Value, Recurring [Member] \| Level 2 [Member] \| Not Designated as Hedging Instrument [Member]
Measured on a recurring basis:
Energy derivative assets	0	0
Energy derivative liabilities	0	0
Fair Value, Recurring [Member] \| Level 3 [Member]
Measured on a recurring basis:
ARO Trust investments	0	0
Fair Value, Recurring [Member] \| Level 3 [Member] \| Designated as Hedging Instrument [Member]
Measured on a recurring basis:
Energy derivative assets	0
Fair Value, Recurring [Member] \| Level 3 [Member] \| Not Designated as Hedging Instrument [Member]
Measured on a recurring basis:
Energy derivative assets	0	0
Energy derivative liabilities	(2)	$ (2)
WilTel Guarantee [Member]
Additional disclosures:
Guarantor Obligations, Maximum Exposure, Undiscounted	28
Indemnification Agreement [Member] \| Carrying Amount [Member]
Additional disclosures:
Guarantees	$ 0

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

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Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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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.

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