Fair Value Measurements (Fair Value by Level) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Assets at fair value
Nuclear decommissioning trusts	$ 4,334	$ 4,440
Southern California Edison
Assets at fair value
Nuclear decommissioning trusts	$ 4,334	$ 4,440
Liabilities at fair value
Percentage of equity investments located in the United States	70.00%	69.00%
Collateralized mortgage obligations and other asset backed securities	$ 113	$ 102
Payables, net, related to investments	68	59
Southern California Edison | Fair Value, Measurements, Recurring
Assets at fair value
Netting and Collateral	(2)	(1)
Derivative contracts	95	110
Other	33	495
Nuclear decommissioning trusts	4,402	4,499
Total assets	4,530	5,104
Liabilities at fair value
Derivative contracts	1	1
Netting and Collateral	(3)	(2)
Total liabilities	1	1
Net assets	4,529	5,103
Total assets, netting and collateral	1	1
Southern California Edison | Fair Value, Measurements, Recurring | Stocks
Assets at fair value
Nuclear decommissioning trusts	1,520	1,596
Southern California Edison | Fair Value, Measurements, Recurring | Fixed income
Assets at fair value
Nuclear decommissioning trusts	2,715	2,730
Southern California Edison | Fair Value, Measurements, Recurring | Short-term investments, primarily cash equivalents
Assets at fair value
Nuclear decommissioning trusts	167	173
Southern California Edison | Fair Value, Measurements, Recurring | Level 1
Assets at fair value
Gross amounts recognized	0	0
Other	12	495
Nuclear decommissioning trusts	2,655	2,762
Total assets	2,667	3,257
Liabilities at fair value
Derivative contracts	0	0
Total liabilities	0	0
Net assets	2,667	3,257
Southern California Edison | Fair Value, Measurements, Recurring | Level 1 | Stocks
Assets at fair value
Nuclear decommissioning trusts	1,520	1,596
Southern California Edison | Fair Value, Measurements, Recurring | Level 1 | Fixed income
Assets at fair value
Nuclear decommissioning trusts	1,076	1,065
Southern California Edison | Fair Value, Measurements, Recurring | Level 1 | Short-term investments, primarily cash equivalents
Assets at fair value
Nuclear decommissioning trusts	59	101
Southern California Edison | Fair Value, Measurements, Recurring | Level 2
Assets at fair value
Gross amounts recognized	15	9
Other	21	0
Nuclear decommissioning trusts	1,747	1,737
Total assets	1,783	1,746
Liabilities at fair value
Derivative contracts	3	2
Total liabilities	3	2
Net assets	1,780	1,744
Southern California Edison | Fair Value, Measurements, Recurring | Level 2 | Stocks
Assets at fair value
Nuclear decommissioning trusts	0	0
Southern California Edison | Fair Value, Measurements, Recurring | Level 2 | Fixed income
Assets at fair value
Nuclear decommissioning trusts	1,639	1,665
Southern California Edison | Fair Value, Measurements, Recurring | Level 2 | Short-term investments, primarily cash equivalents
Assets at fair value
Nuclear decommissioning trusts	108	72
Southern California Edison | Fair Value, Measurements, Recurring | Level 3
Assets at fair value
Gross amounts recognized	82	102
Other	0	0
Nuclear decommissioning trusts	0	0
Total assets	82	102
Liabilities at fair value
Derivative contracts	1	1
Total liabilities	1	1
Net assets	81	101
Southern California Edison | Fair Value, Measurements, Recurring | Level 3 | Stocks
Assets at fair value
Nuclear decommissioning trusts	0	0
Southern California Edison | Fair Value, Measurements, Recurring | Level 3 | Fixed income
Assets at fair value
Nuclear decommissioning trusts	0	0
Southern California Edison | Fair Value, Measurements, Recurring | Level 3 | Short-term investments, primarily cash equivalents
Assets at fair value
Nuclear decommissioning trusts	$ 0	$ 0