Fair Value Measurements (Fair Value by Level) (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Assets and Liabilities at Fair Values
Money market funds	$ 36	$ 37
Assets at fair value
Nuclear decommissioning trusts	4,290	4,331
Level 1
Assets and Liabilities at Fair Values
Money market funds	30	29
Southern California Edison
Assets and Liabilities at Fair Values
Money market funds	7	8
Assets at fair value
Nuclear decommissioning trusts	$ 4,290	$ 4,331	$ 4,896	$ 4,799
Liabilities at fair value
Percentage of equity investments located in the United States (as a percent)	70.00%	70.00%
Collateralized mortgage obligations and other asset backed securities	$ 101	$ 111
Payables, net, related to investments	8	24
Southern California Edison | Fair Value, Measurements, Recurring | Level 1
Assets at fair value
Derivative contracts	0	0
Other	28	28
Nuclear decommissioning trusts	2,440	2,498
Total assets	2,468	2,526
Liabilities at fair value
Derivative contracts	0	0
Total liabilities	0	0
Net assets (liabilities)	2,468	2,526
Southern California Edison | Fair Value, Measurements, Recurring | Level 1 | Stocks
Assets at fair value
Nuclear decommissioning trusts	1,464	1,460
Southern California Edison | Fair Value, Measurements, Recurring | Level 1 | Fixed income
Assets at fair value
Nuclear decommissioning trusts	907	947
Southern California Edison | Fair Value, Measurements, Recurring | Level 1 | Short-term investments, primarily cash equivalents
Assets at fair value
Nuclear decommissioning trusts	69	91
Southern California Edison | Fair Value, Measurements, Recurring | Level 2
Assets at fair value
Derivative contracts	0	0
Other	0	0
Nuclear decommissioning trusts	1,858	1,857
Total assets	1,858	1,857
Liabilities at fair value
Derivative contracts	21	22
Total liabilities	21	22
Net assets (liabilities)	1,837	1,835
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	1,810	1,776
Southern California Edison | Fair Value, Measurements, Recurring | Level 2 | Short-term investments, primarily cash equivalents
Assets at fair value
Nuclear decommissioning trusts	48	81
Southern California Edison | Fair Value, Measurements, Recurring | Level 3
Assets at fair value
Derivative contracts	143	163
Other	0	0
Nuclear decommissioning trusts	0	0
Total assets	143	163
Liabilities at fair value
Derivative contracts	1,356	1,311
Total liabilities	1,356	1,311
Net assets (liabilities)	(1,213)	(1,148)
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
Southern California Edison | Fair Value, Measurements, Recurring | Gross amounts offset in the consolidated balance sheets
Assets at fair value
Derivative contracts	0	0
Other	0	0
Nuclear decommissioning trusts	0	0
Total assets	0	0
Liabilities at fair value
Derivative contracts	(11)	(15)
Total liabilities	(11)	(15)
Net assets (liabilities)	11	15
Southern California Edison | Fair Value, Measurements, Recurring | Gross amounts offset in the consolidated balance sheets | Stocks
Assets at fair value
Nuclear decommissioning trusts	0	0
Southern California Edison | Fair Value, Measurements, Recurring | Gross amounts offset in the consolidated balance sheets | Fixed income
Assets at fair value
Nuclear decommissioning trusts	0	0
Southern California Edison | Fair Value, Measurements, Recurring | Gross amounts offset in the consolidated balance sheets | Short-term investments, primarily cash equivalents
Assets at fair value
Nuclear decommissioning trusts	0	0
Southern California Edison | Fair Value, Measurements, Recurring | Total
Assets at fair value
Derivative contracts	143	163
Other	28	28
Nuclear decommissioning trusts	4,298	4,355
Total assets	4,469	4,546
Liabilities at fair value
Derivative contracts	1,366	1,318
Total liabilities	1,366	1,318
Net assets (liabilities)	3,103	3,228
Southern California Edison | Fair Value, Measurements, Recurring | Total | Stocks
Assets at fair value
Nuclear decommissioning trusts	1,464	1,460
Southern California Edison | Fair Value, Measurements, Recurring | Total | Fixed income
Assets at fair value
Nuclear decommissioning trusts	2,717	2,723
Southern California Edison | Fair Value, Measurements, Recurring | Total | Short-term investments, primarily cash equivalents
Assets at fair value
Nuclear decommissioning trusts	$ 117	$ 172