Fair Value Measurements Recurring Measurements and Additional (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016
Additional disclosures:
Fair Value, Level 1 to level 2 Transfers, Amount	$ 0		$ 0
Fair Value, Level 2 to level 1 Transfers, Amount	0		$ 0
Carrying Amount [Member]
Additional disclosures:
Other receivables	5	$ 15
Long-term debt	(21,825)	(23,409)
Guarantees	(44)	(44)
Fair Value [Member]
Additional disclosures:
Other receivables	5	15
Long-term debt	(23,055)	(24,090)
Guarantees	(31)	(30)
Level 1 [Member]
Additional disclosures:
Other receivables	5	15
Long-term debt	0	0
Guarantees	0	0
Level 2 [Member]
Additional disclosures:
Other receivables	0	0
Long-term debt	(23,055)	(24,090)
Guarantees	(15)	(14)
Level 3 [Member]
Additional disclosures:
Other receivables	0	0
Long-term debt	0	0
Guarantees	(16)	(16)
Fair Value, Measurements, Recurring [Member] | Carrying Amount [Member]
Measured on a recurring basis:
ARO Trust investments	112	96
Fair Value, Measurements, Recurring [Member] | Carrying Amount [Member] | Designated as Hedging Instrument [Member]
Measured on a recurring basis:
Energy derivatives assets	5	2
Fair Value, Measurements, Recurring [Member] | Carrying Amount [Member] | Not Designated as Hedging Instrument [Member]
Measured on a recurring basis:
Energy derivatives assets	2	1
Energy derivatives liabilities	(4)	(6)
Fair Value, Measurements, Recurring [Member] | Fair Value [Member]
Measured on a recurring basis:
ARO Trust investments	112	96
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Designated as Hedging Instrument [Member]
Measured on a recurring basis:
Energy derivatives assets	5	2
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Not Designated as Hedging Instrument [Member]
Measured on a recurring basis:
Energy derivatives assets	2	1
Energy derivatives liabilities	(4)	(6)
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Measured on a recurring basis:
ARO Trust investments	112	96
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Designated as Hedging Instrument [Member]
Measured on a recurring basis:
Energy derivatives assets	5	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Not Designated as Hedging Instrument [Member]
Measured on a recurring basis:
Energy derivatives assets	1	0
Energy derivatives liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Measured on a recurring basis:
ARO Trust investments	0	0
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Designated as Hedging Instrument [Member]
Measured on a recurring basis:
Energy derivatives assets	0	2
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Not Designated as Hedging Instrument [Member]
Measured on a recurring basis:
Energy derivatives assets	0	0
Energy derivatives liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Measured on a recurring basis:
ARO Trust investments	0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Designated as Hedging Instrument [Member]
Measured on a recurring basis:
Energy derivatives assets	0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Not Designated as Hedging Instrument [Member]
Measured on a recurring basis:
Energy derivatives assets	1	1
Energy derivatives liabilities	(4)	$ (6)
WilTel Guarantee [Member]
Additional disclosures:
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 31