Long-Term Debt (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2018	Sep. 30, 2017	Aug. 24, 2018	Jun. 15, 2018	Mar. 28, 2018	Mar. 15, 2018	Mar. 05, 2018	Dec. 31, 2017	Jul. 03, 2017	Jun. 05, 2017	Apr. 03, 2017	Feb. 23, 2017
Long-term Debt
Debt issuance costs	$ (131)							$ (122)
Net unamortized debt premium (discount)	(62)				$ (7)			(24)	$ (3)			$ (30)
Total long-term debt, including current portion	22,414							20,935
Long-term debt due within one year	(47)							(501)
Long-term debt	22,367							20,434
4.875% Senior Unsecured Notes due 2024 [Member]
Long-term Debt
Long-term debt interest rate					4.875%
Transcontinental Gas Pipe Line Company, LLC [Member]
Long-term Debt
Other financing obligations	1,067							231
Transcontinental Gas Pipe Line Company, LLC [Member] | 6.05% Senior Unsecured Notes due 2018 [Member]
Long-term Debt
Long-term debt	0							$ 250
Long-term debt interest rate				6.05%				6.05%
Transcontinental Gas Pipe Line Company, LLC [Member] | 7.08% Debentures due 2026 [Member]
Long-term Debt
Long-term debt	$ 8							$ 8
Long-term debt interest rate	7.08%
Transcontinental Gas Pipe Line Company, LLC [Member] | 7.25% Debentures due 2026 [Member]
Long-term Debt
Long-term debt	$ 200							200
Long-term debt interest rate	7.25%
Transcontinental Gas Pipe Line Company, LLC [Member] | 7.85% Senior Unsecured Notes Due 2026 [Member]
Long-term Debt
Long-term debt	$ 1,000							1,000
Long-term debt interest rate	7.85%
Transcontinental Gas Pipe Line Company, LLC [Member] | 4% Senior Unsecured Notes Due 2028 [Member]
Long-term Debt
Long-term debt	$ 400							0
Long-term debt interest rate	4.00%					4.00%
Transcontinental Gas Pipe Line Company, LLC [Member] | 5.4% Senior Unsecured Notes due 2041 [Member]
Long-term Debt
Long-term debt	$ 375							375
Long-term debt interest rate	5.40%
Transcontinental Gas Pipe Line Company, LLC [Member] | 4.45% Senior Unsecured Notes due 2042 [Member]
Long-term Debt
Long-term debt	$ 400							400
Long-term debt interest rate	4.45%
Transcontinental Gas Pipe Line Company, LLC [Member] | 4.6%SeniorUnsecuredNotesDue2048 [Member]
Long-term Debt
Long-term debt	$ 600							0
Long-term debt interest rate	4.60%					4.60%
Transcontinental Gas Pipe Line Company, LLC [Member] | Dalton [Member]
Long-term Debt
Other financing obligations	$ 260							231
Capitalized Construction Costs	100.00%
Debt Instrument, Term		35 years
Transcontinental Gas Pipe Line Company, LLC [Member] | AtlanticSunrise [Member]
Long-term Debt
Other financing obligations	$ 807
Capitalized Construction Costs	100.00%
Debt Instrument, Term	20 years
Northwest Pipeline LLC [Member] | 6.05% Senior Unsecured Notes due 2018 [Member]
Long-term Debt
Long-term debt	$ 0							$ 250
Long-term debt interest rate				6.05%				6.05%
Northwest Pipeline LLC [Member] | 7.125% Debentures due 2025 [Member]
Long-term Debt
Long-term debt	$ 85							$ 85
Long-term debt interest rate	7.125%
Northwest Pipeline LLC [Member] | 4% Senior Unsecured Notes Due 2027 [Member]
Long-term Debt
Long-term debt	$ 500							250
Long-term debt interest rate	4.00%		4.00%								4.00%
Williams Partners L.P. [Member] | 3.75% Senior Unsecured Notes Due 2027 [Member]
Long-term Debt
Long-term debt interest rate										3.75%
Williams Partners L.P. [Member] | 4.85%SeniorUnsecuredNotesDue2048 [Member]
Long-term Debt
Long-term debt interest rate							4.85%
The Williams Companies, Inc. [Member]
Long-term Debt
Credit facility loans	$ 160							270
The Williams Companies, Inc. [Member] | 5.25% Senior Unsecured Notes due 2020 [Member]
Long-term Debt
Long-term debt	$ 1,500							1,500
Long-term debt interest rate	5.25%
The Williams Companies, Inc. [Member] | 4.125% Senior Unsecured Notes due 2020 [Member]
Long-term Debt
Long-term debt	$ 600							600
Long-term debt interest rate	4.125%
The Williams Companies, Inc. [Member] | 4% Senior Unsecured Notes due 2021 [Member]
Long-term Debt
Long-term debt	$ 500							500
Long-term debt interest rate	4.00%
The Williams Companies, Inc. [Member] | 7.875% Senior Unsecured Notes due 2021 [Member]
Long-term Debt
Long-term debt	$ 371							371
Long-term debt interest rate	7.875%
The Williams Companies, Inc. [Member] | 3.35% Senior Unsecured Notes due 2022 [Member]
Long-term Debt
Long-term debt	$ 750							750
Long-term debt interest rate	3.35%
The Williams Companies, Inc. [Member] | 3.6% Senior Unsecured Notes due 2022 [Member]
Long-term Debt
Long-term debt	$ 1,250							1,250
Long-term debt interest rate	3.60%
The Williams Companies, Inc. [Member] | 3.7% Senior Unsecured Notes due 2023 [Member]
Long-term Debt
Long-term debt	$ 850							850
Long-term debt interest rate	3.70%
The Williams Companies, Inc. [Member] | 4.5% Senior Unsecured Notes due 2023 [Member]
Long-term Debt
Long-term debt	$ 600							600
Long-term debt interest rate	4.50%
The Williams Companies, Inc. [Member] | 4.3% Senior Unsecured Notes Due 2024 [Member]
Long-term Debt
Long-term debt	$ 1,000							1,000
Long-term debt interest rate	4.30%
The Williams Companies, Inc. [Member] | 4.55% Senior Unsecured Notes due 2024 [Member]
Long-term Debt
Long-term debt	$ 1,250							1,250
Long-term debt interest rate	4.55%
The Williams Companies, Inc. [Member] | 4.875% Senior Unsecured Notes due 2024 [Member]
Long-term Debt
Long-term debt	$ 0							$ 750
Long-term debt interest rate								4.875%
The Williams Companies, Inc. [Member] | 3.9% Senior Unsecured Notes due 2025 [Member]
Long-term Debt
Long-term debt	$ 750							$ 750
Long-term debt interest rate	3.90%
The Williams Companies, Inc. [Member] | 4% Senior Unsecured Notes due 2025 [Member]
Long-term Debt
Long-term debt	$ 750							750
Long-term debt interest rate	4.00%
The Williams Companies, Inc. [Member] | 3.75% Senior Unsecured Notes Due 2027 [Member]
Long-term Debt
Long-term debt	$ 1,450							1,450
Long-term debt interest rate	3.75%
The Williams Companies, Inc. [Member] | 7.5% Debentures due 2031 [Member]
Long-term Debt
Long-term debt	$ 339							339
Long-term debt interest rate	7.50%
The Williams Companies, Inc. [Member] | 7.75% Senior Unsecured Notes due 2031 [Member]
Long-term Debt
Long-term debt	$ 252							252
Long-term debt interest rate	7.75%
The Williams Companies, Inc. [Member] | 8.75% Senior Unsecured Notes due 2032 [Member]
Long-term Debt
Long-term debt	$ 445							445
Long-term debt interest rate	8.75%
The Williams Companies, Inc. [Member] | 6.3% Senior Unsecured Notes due 2040 [Member]
Long-term Debt
Long-term debt	$ 1,250							1,250
Long-term debt interest rate	6.30%
The Williams Companies, Inc. [Member] | 5.8% Senior Unsecured Notes due 2043 [Member]
Long-term Debt
Long-term debt	$ 400							400
Long-term debt interest rate	5.80%
The Williams Companies, Inc. [Member] | 5.4% Senior Unsecured Notes Due 2044 [Member]
Long-term Debt
Long-term debt	$ 500							500
Long-term debt interest rate	5.40%
The Williams Companies, Inc. [Member] | 5.75% Senior Unsecured Notes due 2044 [Member]
Long-term Debt
Long-term debt	$ 650							650
Long-term debt interest rate	5.75%
The Williams Companies, Inc. [Member] | Various - 7.625% to 10.25% Senior Unsecured Notes and Debentures due 2019 to 2027 Minimum Interest Rate [Member]
Long-term Debt
Long-term debt interest rate	7.625%
The Williams Companies, Inc. [Member] | Various - 7.625% to 10.25% Senior Unsecured Notes and Debentures due 2019 to 2027 Maximum Interest Rate [Member]
Long-term Debt
Long-term debt interest rate	10.25%
The Williams Companies, Inc. [Member] | 4.9% Senior Unsecured Notes due 2045 [Member]
Long-term Debt
Long-term debt	$ 500							500
Long-term debt interest rate	4.90%
The Williams Companies, Inc. [Member] | 5.1% Senior Unsecured Notes due 2045 [Member]
Long-term Debt
Long-term debt	$ 1,000							1,000
Long-term debt interest rate	5.10%
The Williams Companies, Inc. [Member] | 4.85%SeniorUnsecuredNotesDue2048 [Member]
Long-term Debt
Long-term debt	$ 800							0
Long-term debt interest rate	4.85%
The Williams Companies, Inc. [Member] | Various - 7.625% to 10.25% Senior Unsecured Notes and Debentures due 2019 to 2027 [Member]
Long-term Debt
Long-term debt	$ 55							$ 55