Fair Value Measurements (Fair Value by Level) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Assets at fair value
Nuclear decommissioning trusts	$ 4,833	$ 4,562
SCE
Assets at fair value
Nuclear decommissioning trusts	$ 4,833	$ 4,562
Liabilities at fair value
Percentage of equity investments located in the United States (as a percent)	71.00%	72.00%
Collateralized mortgage obligations and other asset backed securities	$ 29	$ 46
Payables, net, related to investments	(206)	(111)
SCE | Fair Value, Measurements, Recurring
Assets at fair value
Netting and Collateral	(18)	(15)
Derivative contracts, net	108	87
Other	62	18
Nuclear decommissioning trusts	5,039	4,673
Total assets	5,209	4,778
Liabilities at fair value
Netting and Collateral	(22)	(15)
Derivative contracts, net	0	1
Total liabilities	0	1
Net assets	5,209	4,777
Cash collateral posted	4	0
SCE | Fair Value, Measurements, Recurring | Level 1
Assets at fair value
Derivative contracts	0	0
Other	39	4
Nuclear decommissioning trusts	2,874	2,601
Total assets	2,913	2,605
Liabilities at fair value
Derivative contracts	0	0
Total liabilities	0	0
Net assets	2,913	2,605
SCE | Fair Value, Measurements, Recurring | Level 2
Assets at fair value
Derivative contracts	6	19
Other	23	14
Nuclear decommissioning trusts	2,165	2,072
Total assets	2,194	2,105
Liabilities at fair value
Derivative contracts	10	11
Total liabilities	10	11
Net assets	2,184	2,094
SCE | Fair Value, Measurements, Recurring | Level 3
Assets at fair value
Derivative contracts	120	83
Other	0	0
Nuclear decommissioning trusts	0	0
Total assets	120	83
Liabilities at fair value
Derivative contracts	12	5
Total liabilities	12	5
Net assets	108	78
SCE | Fair Value, Measurements, Recurring | Stocks
Assets at fair value
Nuclear decommissioning trusts	1,908	1,765
SCE | Fair Value, Measurements, Recurring | Stocks | Level 1
Assets at fair value
Nuclear decommissioning trusts	1,908	1,765
SCE | Fair Value, Measurements, Recurring | Stocks | Level 2
Assets at fair value
Nuclear decommissioning trusts	0	0
SCE | Fair Value, Measurements, Recurring | Stocks | Level 3
Assets at fair value
Nuclear decommissioning trusts	0	0
SCE | Fair Value, Measurements, Recurring | Fixed Income
Assets at fair value
Nuclear decommissioning trusts	2,632	2,762
SCE | Fair Value, Measurements, Recurring | Fixed Income | Level 1
Assets at fair value
Nuclear decommissioning trusts	519	738
SCE | Fair Value, Measurements, Recurring | Fixed Income | Level 2
Assets at fair value
Nuclear decommissioning trusts	2,113	2,024
SCE | Fair Value, Measurements, Recurring | Fixed Income | Level 3
Assets at fair value
Nuclear decommissioning trusts	0	0
SCE | Fair Value, Measurements, Recurring | Short-term investments, primarily cash equivalents
Assets at fair value
Nuclear decommissioning trusts	499	146
SCE | Fair Value, Measurements, Recurring | Short-term investments, primarily cash equivalents | Level 1
Assets at fair value
Nuclear decommissioning trusts	447	98
SCE | Fair Value, Measurements, Recurring | Short-term investments, primarily cash equivalents | Level 2
Assets at fair value
Nuclear decommissioning trusts	52	48
SCE | Fair Value, Measurements, Recurring | Short-term investments, primarily cash equivalents | Level 3
Assets at fair value
Nuclear decommissioning trusts	$ 0	$ 0