Fair Value Measurements Nonrecurring Measurements (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Fair Value Assets Measured On Nonrecurring Basis [Abstract]
Impairment of equity-method investments		$ 0	$ 112
Williams Partners [Member] | Delaware Basin Gas Gathering System [Member]
Fair Value Assets Measured On Nonrecurring Basis [Abstract]
Impairment of equity-method investments			59
Fair Value, Measurements, Nonrecurring [Member] | Impairment Of Equity-Method Investments [Member]
Fair Value Assets Measured On Nonrecurring Basis [Abstract]
Impairment of equity-method investments		0	112
Fair Value, Measurements, Nonrecurring [Member] | Level 3 [Member] | Investments [Member]
Fair Value Assets Measured On Nonrecurring Basis [Abstract]
Fair value of investment			0
Fair Value, Measurements, Nonrecurring [Member] | Level 3 [Member] | Investments [Member] | Williams Partners [Member]
Fair Value Assets Measured On Nonrecurring Basis [Abstract]
Fair value of investment	[1]		$ 1,294
Fair Value, Measurements, Nonrecurring [Member] | Level 3 [Member] | Investments [Member] | Williams Partners [Member] | Minimum [Member]
Fair Value Assets Measured On Nonrecurring Basis [Abstract]
Discount rate			13.00%
Fair Value, Measurements, Nonrecurring [Member] | Level 3 [Member] | Investments [Member] | Williams Partners [Member] | Maximum [Member]
Fair Value Assets Measured On Nonrecurring Basis [Abstract]
Discount rate			13.30%
Fair Value, Measurements, Nonrecurring [Member] | Level 3 [Member] | Impairment Of Equity-Method Investments [Member]
Fair Value Assets Measured On Nonrecurring Basis [Abstract]
Impairment of equity-method investments		0	$ 3
Fair Value, Measurements, Nonrecurring [Member] | Level 3 [Member] | Impairment Of Equity-Method Investments [Member] | Williams Partners [Member]
Fair Value Assets Measured On Nonrecurring Basis [Abstract]
Impairment of equity-method investments	[1]	$ 0	$ 109

[1] Relates to equity-method investments in DBJV and Laurel Mountain. Our carrying values in these equity-method investments had been written down to fair value at December 31, 2015. Our first-quarter 2016 analysis reflected higher discount rates for both of these investments, along with lower natural gas prices for Laurel Mountain. We estimated the fair value of these investments using an income approach based on expected future cash flows and appropriate discount rates. The determination of estimated future cash flows involved significant assumptions regarding gathering volumes and related capital spending. Discount rates utilized ranged from 13.0 percent to 13.3 percent and reflected increases in our estimated cost of capital, revised estimates of expected future cash flows, and risks associated with the underlying businesses.