GENERAL INFORMATION AND OTHER FINANCIAL DATA - DUE TO DUE FROM AFFILIATES (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)		Sep. 30, 2021 MXN ($)	Mar. 31, 2021
Related Party Transaction [Line Items]
Due from unconsolidated affiliates - current	$ 30,000,000	$ 20,000,000	[1]
Due from unconsolidated affiliates - noncurrent	684,000,000	780,000,000	[1]
Due to unconsolidated affiliates, current	(42,000,000)	(45,000,000)	[1]
Due to unconsolidated affiliates - noncurrent	(286,000,000)	$ (234,000,000)	[1]
Maximum borrowing capacity	$ 6,685,000,000
ESJ joint venture [Member] | ESJ [Member]
Related Party Transaction [Line Items]
Additional ownership percentage					50.00%
ESJ joint venture [Member] | LIBOR [Member]
Related Party Transaction [Line Items]
Spread on variable rate (as a percent)		1.96%
Interest rate on due from affiliate, noncurrent		2.11%
TAG Pipeline Norte [Member]
Related Party Transaction [Line Items]
Interest rate on due from affiliate, noncurrent	3.06%
TAG Pipeline Norte [Member] | LIBOR [Member]
Related Party Transaction [Line Items]
Spread on variable rate (as a percent)	2.90%
Various Affiliates [Member]
Related Party Transaction [Line Items]
Due to unconsolidated affiliates, current	$ 0	$ (4,000,000)
San Diego Gas and Electric Company [Member]
Related Party Transaction [Line Items]
Due from unconsolidated affiliates - current	1,000,000	0
Due to unconsolidated affiliates, current	(61,000,000)	(64,000,000)	[1]
Maximum borrowing capacity	1,500,000,000
San Diego Gas and Electric Company [Member] | Due to/from Sempra Energy [Member]
Related Party Transaction [Line Items]
Due to unconsolidated affiliates, current	(45,000,000)	(38,000,000)
Income taxes due (to) from Sempra Energy	29,000,000	0
San Diego Gas and Electric Company [Member] | Due to/from SoCalGas [Member]
Related Party Transaction [Line Items]
Due to unconsolidated affiliates, current	(9,000,000)	(21,000,000)
San Diego Gas and Electric Company [Member] | Due to/from Other affiliates [Member]
Related Party Transaction [Line Items]
Due to unconsolidated affiliates, current	(7,000,000)	(5,000,000)
Southern California Gas Company [Member]
Related Party Transaction [Line Items]
Due from unconsolidated affiliates - current	11,000,000	22,000,000	[1]
Due to unconsolidated affiliates, current	(45,000,000)	(31,000,000)	[2]
Maximum borrowing capacity	750,000,000
Southern California Gas Company [Member] | Due to/from Sempra Energy [Member]
Related Party Transaction [Line Items]
Due to unconsolidated affiliates, current	(45,000,000)	(31,000,000)
Income taxes due (to) from Sempra Energy	1,000,000	(37,000,000)
Southern California Gas Company [Member] | Due to/from Other affiliates [Member]
Related Party Transaction [Line Items]
Due from unconsolidated affiliates - current	2,000,000	1,000,000
Southern California Gas Company [Member] | Due to/from SDG&E
Related Party Transaction [Line Items]
Due from unconsolidated affiliates - current	9,000,000	21,000,000
Sempra Mexico [Member]
Related Party Transaction [Line Items]
Due to unconsolidated affiliates - noncurrent	(286,000,000)	(234,000,000)
Sempra Mexico [Member] | ESJ joint venture [Member]
Related Party Transaction [Line Items]
Due from unconsolidated affiliates - noncurrent	0	85,000,000
Accrued interest receivable		1,000,000
Sempra Mexico [Member] | IMG [Member]
Related Party Transaction [Line Items]
Due from unconsolidated affiliates - noncurrent	684,000,000	695,000,000
Due from affiliates, allowance for credit loss	1,000,000	3,000,000
Accrued interest receivable	2,000,000	2,000,000
Maximum borrowing capacity	$ 689,000,000			$ 14,200,000,000
Sempra Mexico [Member] | IMG [Member] | Interbank Equilibrium Rate [Member]
Related Party Transaction [Line Items]
Spread on variable rate (as a percent)	2.20%
Interest rate on due from affiliate, noncurrent	7.02%
Sempra Mexico [Member] | TAG Pipeline Norte [Member]
Related Party Transaction [Line Items]
Stated rate of debt (as a percent)	5.50%			5.50%
Sempra Mexico [Member] | TAG JV Notes [Member]
Related Party Transaction [Line Items]
Due to unconsolidated affiliates - noncurrent	$ (174,000,000)	(166,000,000)
Stated rate of debt (as a percent)	5.74%			5.74%
Other Long term Debt Currently Through December 2021 [Member] | Sempra Mexico [Member] | TAG Pipeline Norte [Member]
Related Party Transaction [Line Items]
Due to unconsolidated affiliates, current	$ (42,000,000)	(41,000,000)
Due to unconsolidated affiliates - noncurrent	(71,000,000)	(68,000,000)
Other Long term Debt Currently Through January 2024 [Member] | Sempra Mexico [Member] | TAG Pipeline Norte [Member]
Related Party Transaction [Line Items]
Due to unconsolidated affiliates - noncurrent	(21,000,000)	0
Five Point Five Percent Notes Due 2029 | Sempra Mexico [Member] | TAG Pipeline Norte [Member]
Related Party Transaction [Line Items]
Due to unconsolidated affiliates - noncurrent	$ (20,000,000)	$ 0
Stated rate of debt (as a percent)	5.50%			5.50%

[1] Derived from audited financial statements.

[2] Derived from audited financial statements.