Contingent Liabilities (Details) - USD ($) $ in Millions	May 20, 2016	Sep. 30, 2017
Loss Contingencies [Line Items]
Accrued environmental loss liabilities		$ 40
Energy Transfer Merger [Member]
Loss Contingencies [Line Items]
Loss contingency, damages sought, value	$ 1,480
Gas Pipeline [Member]
Loss Contingencies [Line Items]
Accrued environmental loss liabilities		8
Natural Gas Underground Storage Facilities [Member]
Loss Contingencies [Line Items]
Accrued environmental loss liabilities		8
Former Operations [Member]
Loss Contingencies [Line Items]
Accrued environmental loss liabilities		24
Williams Partners [Member] | General Liability [Member] | Geismar Incident [Member]
Loss Contingencies [Line Items]
Insurance deductibles		2
Aggregate limit of insurance		610
Maximum [Member] | Former Alaska Refinery [Member]
Loss Contingencies [Line Items]
Loss contingency, range of possible loss, maximum		$ 32