Summary of Significant Accounting Policies (Cash, Cash Equivalents and Restricted Cash) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restricted Cash and Cash Equivalents Items [Line Items]
Money market funds	$ 116	$ 1,024
Book balances reclassified to accounts payable	65	64
Restricted cash	8	41
Cash and cash equivalents	144	1,091
Short-term restricted cash	8	40
Long-term restricted cash	0	1
Total cash, cash equivalents, and restricted cash	152	1,132	$ 114	$ 168
SCE
Restricted Cash and Cash Equivalents Items [Line Items]
Money market funds	1	483
Book balances reclassified to accounts payable	65	63
Cash and cash equivalents	21	515
Short-term restricted cash	1	0
Total cash, cash equivalents, and restricted cash	$ 22	$ 515	$ 40	$ 32