Debt, Financing Arrangements and Leases (Details) - USD ($)			1 Months Ended	12 Months Ended
	Oct. 01, 2018	Jun. 15, 2018	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jul. 13, 2018	Mar. 15, 2018
Debt Instrument [Line Items]
Total long-term debt, including current portion				$ 4,049,786,000	$ 2,463,426,000
Other financing obligation				1,067,286,000	230,926,000
Unamortized debt issuance costs				(24,242,000)	(15,377,000)
Unamortized debt premium and discount, net				(11,137,000)	(5,043,000)
Long-term debt due within one year				15,419,000	251,430,000
Total long-term debt				3,998,988,000	2,191,576,000
Long-term Debt, Fiscal Year Maturity [Abstract]
2019				15,419,000
2020				17,042,000
2021				18,837,000
2022				20,821,000
2023				23,014,000
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2019				9,044,000
2020				9,014,000
2021				8,865,000
2022				8,808,000
2023				8,829,000
Thereafter				65,107,000
Total net minimum obligations				109,667,000
Operating leases, rent expense				10,800,000	11,000,000	$ 10,600,000
6.05% due 2018 [Member]
Debt Instrument [Line Items]
Long-term debt interest rate		6.05%
Long-Term Debt, retired		$ 250,000,000
4.0% due 2028 [Member]
Debt Instrument [Line Items]
Long-term debt face amount								$ 400,000,000
Long-term debt interest rate								4.00%
4.6 % due 2048 [Member]
Debt Instrument [Line Items]
Long-term debt face amount								$ 600,000,000
Long-term debt interest rate								4.60%
10% due 2052 [Member]
Debt Instrument [Line Items]
Long-term debt interest rate			9.00%
Dalton Expansion Project [Member]
Debt Instrument [Line Items]
Other financing obligation			$ 235,800,000	29,800,000
Long-term debt face amount				258,100,000	229,400,000
Debt Instrument, Term			35 years
Other Long-term Debt, Current				$ 1,900,000	1,600,000
Percent Of Construction Costs Capitalized				100.00%
Atlantic Sunrise Project [Member]
Debt Instrument [Line Items]
Other financing obligation	$ 810,300,000			$ 20,500,000
Long-term debt face amount				793,800,000
Long-term debt interest rate	10.00%
Debt Instrument, Term	20 years
Other Long-term Debt, Current				$ 13,500,000
Percent Of Construction Costs Capitalized				100.00%
Debentures
Debt Instrument [Line Items]
Total long-term debt, including current portion				$ 207,500,000	207,500,000
Debentures | 7.08% due 2026 [Member]
Debt Instrument [Line Items]
Total long-term debt, including current portion				7,500,000	7,500,000
Debentures | 7.25% due 2026 [Member]
Debt Instrument [Line Items]
Total long-term debt, including current portion				200,000,000	200,000,000
Notes
Debt Instrument [Line Items]
Total long-term debt, including current portion				2,775,000,000	2,025,000,000
Notes | 6.05% due 2018 [Member]
Debt Instrument [Line Items]
Total long-term debt, including current portion				0	250,000,000
Notes | 7.85% due 2026
Debt Instrument [Line Items]
Total long-term debt, including current portion				1,000,000,000	1,000,000,000
Notes | 4.0% due 2028 [Member]
Debt Instrument [Line Items]
Total long-term debt, including current portion				400,000,000	0
Notes | 5.4% due 2041 [Member]
Debt Instrument [Line Items]
Total long-term debt, including current portion				375,000,000	375,000,000
Notes | 4.45% due 2042 [Member]
Debt Instrument [Line Items]
Total long-term debt, including current portion				400,000,000	400,000,000
Notes | 4.6 % due 2048 [Member]
Debt Instrument [Line Items]
Total long-term debt, including current portion				600,000,000	$ 0
$4.5 billion credit facility [Member]
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity							$ 500,000,000
$4.5 billion credit facility [Member] | Williams Companies Inc [Member]
Line of Credit Facility [Line Items]
Letters of credit outstanding, amount				0
Line of credit facility, amount outstanding				160,000,000
Line of credit facility, maximum borrowing capacity							4,500,000,000
Additional amount by which credit facility can be increased							500,000,000
Swing Line Advances [Member] | Williams Companies Inc [Member]
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity							200,000,000
Commercial paper [Member] | Williams Companies Inc [Member]
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity							4,000,000,000
Commercial paper				$ 0
Letter of Credit [Member]
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity							500,000,000
Letter of Credit [Member] | Williams Companies Inc [Member]
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity							$ 1,000,000,000