SIGNIFICANT ACCOUNTING POLICIES AND OTHER FINANCIAL DATA - PRINCIPLES OF CONSOLIDATION (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Assets, Current [Abstract]
Regulatory assets	$ 325	$ 348	[1]
Greenhouse gas allowances	299	40	[1]
Regulatory balancing accounts – undercollected		0
Other	136	142	[1]
Other Assets [Abstract]
Regulatory assets	1,517	3,414	[1]
Greenhouse gas allowances	93	295	[1]
Sundry	792	520	[1]
Liabilities, Current [Abstract]
Regulatory liabilities	109	122	[1]
Greenhouse gas obligations	299	40	[1]
Regulatory balancing accounts – overcollected		0
Other	545	517	[1]
Deferred Credits and Other Liabilities [Abstract]
Regulatory liabilities	3,922	2,876	[1]
Greenhouse gas obligations	0	171	[1]
Regulatory liabilities arising from removal obligations		0
Deferred credits and other	1,136	1,173	[1]
As previously reported [Member]
Assets, Current [Abstract]
Regulatory assets		0
Greenhouse gas allowances		0
Regulatory balancing accounts – undercollected		259
Other		271
Other Assets [Abstract]
Greenhouse gas allowances		0
Sundry		815
Liabilities, Current [Abstract]
Regulatory liabilities		0
Greenhouse gas obligations		0
Regulatory balancing accounts – overcollected		122
Other		557
Deferred Credits and Other Liabilities [Abstract]
Regulatory liabilities		0
Greenhouse gas obligations		0
Regulatory liabilities arising from removal obligations		2,697
Deferred credits and other		1,523
San Diego Gas and Electric Company [Member]
Assets, Current [Abstract]
Regulatory assets	316	340	[1]
Greenhouse gas allowances	116	16	[1]
Regulatory balancing accounts – undercollected		0
Other	4	3	[1]
Other Assets [Abstract]
Regulatory assets	451	2,012	[1]
Greenhouse gas allowances	83	182	[1]
Deferred taxes recoverable in rates		0
Other regulatory assets		0
Sundry	328	176	[1]
Liabilities, Current [Abstract]
Regulatory liabilities	18	0	[1]
Greenhouse gas obligations	116	16	[1]
Other	46	66	[1]
Deferred Credits and Other Liabilities [Abstract]
Regulatory liabilities	2,225	1,725	[1]
Greenhouse gas obligations	0	72	[1]
Regulatory liabilities arising from removal obligations		0
Deferred credits and other	334	349	[1]
San Diego Gas and Electric Company [Member] | As previously reported [Member]
Assets, Current [Abstract]
Regulatory assets		81
Greenhouse gas allowances		0
Regulatory balancing accounts – undercollected		259
Other		19
Other Assets [Abstract]
Regulatory assets		0
Greenhouse gas allowances		0
Deferred taxes recoverable in rates		1,014
Other regulatory assets		998
Sundry		358
Liabilities, Current [Abstract]
Greenhouse gas obligations		0
Other		82
Deferred Credits and Other Liabilities [Abstract]
Regulatory liabilities		0
Greenhouse gas obligations		0
Regulatory liabilities arising from removal obligations		1,725
Deferred credits and other		421
Southern California Gas Company [Member]
Assets, Current [Abstract]
Regulatory assets	9	8	[1]
Greenhouse gas allowances	179	24	[1]
Other	38	39	[1]
Other Assets [Abstract]
Regulatory assets	983	1,331	[1]
Greenhouse gas allowances	9	109	[1]
Regulatory assets arising from pension obligations		0
Other regulatory assets		0
Sundry	364	290	[1]
Liabilities, Current [Abstract]
Regulatory liabilities	91	122	[1]
Greenhouse gas obligations	179	24	[1]
Regulatory balancing accounts – overcollected		0
Other	205	171	[1]
Deferred Credits and Other Liabilities [Abstract]
Regulatory liabilities	1,697	1,151	[1]
Greenhouse gas obligations	0	96	[1]
Regulatory liabilities arising from removal obligations		0
Deferred credits and other	$ 253	246	[1]
Southern California Gas Company [Member] | As previously reported [Member]
Assets, Current [Abstract]
Greenhouse gas allowances		0
Other		63
Other Assets [Abstract]
Regulatory assets		0
Greenhouse gas allowances		0
Regulatory assets arising from pension obligations		742
Other regulatory assets		589
Sundry		399
Liabilities, Current [Abstract]
Regulatory liabilities		0
Greenhouse gas obligations		0
Regulatory balancing accounts – overcollected		122
Other		195
Deferred Credits and Other Liabilities [Abstract]
Regulatory liabilities		0
Greenhouse gas obligations		0
Regulatory liabilities arising from removal obligations		972
Deferred credits and other		$ 521

[1] Reflects reclassifications to conform to current year presentation, which we discuss in Note 1.