Summary of Significant Accounting Policies (Cash, Cash Equivalents and Restricted Cash) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restricted Cash and Cash Equivalents Items [Line Items]
Money market funds	$ 31	$ 116
Book balances reclassified to accounts payable	75	65
Cash and cash equivalents	68	144
Short-term restricted cash	2	8
Total cash, cash equivalents, and restricted cash	70	152	$ 1,132	$ 114
SCE
Restricted Cash and Cash Equivalents Items [Line Items]
Money market funds	0	1
Book balances reclassified to accounts payable	74	65
Cash and cash equivalents	24	21
Short-term restricted cash	0	1
Total cash, cash equivalents, and restricted cash	$ 24	$ 22	$ 515	$ 40