EBP Net Periodic Benefit Cost & OCI (Details 2) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pension Benefits [Member]
Components of net periodic benefit cost:
Service cost	$ 59	$ 40	$ 44
Interest cost	58	62	51
Expected return on plan assets	(75)	(76)	(61)
Amortization of prior service cost (credit)	0	0	1
Amortization of net actuarial loss	42	39	60
Net actuarial (gain) loss from settlements and curtailments	2	1	0
Reclassification to regulatory liability	0	0	0
Net periodic benefit cost	86	66	95
Other changes in plan assets and benefit obligations recognized in other comprehensive income (loss):
Net actuarial gain (loss)	5	(142)	277
Prior service (cost) credit	0	0	0
Amortization of prior service cost (credit)	0	0	1
Amortization of net actuarial loss	42	39	60
Loss from settlements and curtailments	2	1	0
Other changes in plan assets and benefit obligations recognized in other comprehensive income (loss)	49	(102)	338
Amounts included in accumulated other comprehensive income (loss):
Prior service cost (credit) expected to be amortized in next fiscal year	0
Net actuarial (gain) loss expected to be amortized in next fiscal year	31
Other Postretirement Benefits [Member]
Components of net periodic benefit cost:
Service cost	2	2	2
Interest cost	9	10	11
Expected return on plan assets	(12)	(12)	(9)
Amortization of prior service cost (credit)	(17)	(20)	(12)
Amortization of net actuarial loss	2	0	4
Net actuarial (gain) loss from settlements and curtailments	0	(1)	0
Reclassification to regulatory liability	3	4	2
Net periodic benefit cost	(13)	(17)	(2)
Other changes in plan assets and benefit obligations recognized in other comprehensive income (loss):
Net actuarial gain (loss)	8	(18)	23
Prior service (cost) credit	0	(1)	23
Amortization of prior service cost (credit)	(6)	(8)	(4)
Amortization of net actuarial loss	2	0	1
Loss from settlements and curtailments	0	1	0
Other changes in plan assets and benefit obligations recognized in other comprehensive income (loss)	4	(26)	43
Other changes in plan assets and benefit obligations recognized in regulatory (assets) liabilities:
Net actuarial gain (loss) recognized in regulatory liabilities (assets)	10	(2)	62
Prior service credit (cost) recognized in regulatory liabilities (assets)	0	0	36
Amortization of net actuarial loss (gain) from regulatory assets (liabilities)	0	0	3
Amortization of prior service cost (credit) from regulatory assets (liabilities)	(11)	$ (12)	$ (8)
Amounts included in accumulated other comprehensive income (loss):
Prior service cost (credit) expected to be amortized in next fiscal year	(6)
Net actuarial (gain) loss expected to be amortized in next fiscal year	0
Amounts included in regulatory liabilities associated with Transco and Northwest Pipeline
Prior service cost (credit) expected to be amortized in next fiscal year	(9)
Net actuarial (gain) loss expected to be amortized in next fiscal year	$ 0