Condensed Parent Company Financial Statements (Condensed Statements Of Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating expenses	$ 2,676	$ 2,870	$ 2,840
Operating income (loss)	740	778	694
Other (income) and deductions:
Equity earnings from consolidated subsidiaries	(61)	(53)	(55)
Interest expense	275	273	247
Total other (income) and deductions	173	142	124
Income before income taxes	567	636	570
Income tax benefit	(57)	69	48
Net income	624	567	522
Parent Company [Member]
Operating expenses	7	2	5
Operating income (loss)	(7)	(2)	(5)
Other (income) and deductions:
Equity earnings from consolidated subsidiaries	(625)	(562)	(523)
Interest expense	2	9	4
Other	4	7	2
Total other (income) and deductions	(619)	(546)	(517)
Income before income taxes	612	544	512
Income tax benefit	(4)	(15)	(1)
Net income	$ 616	$ 559	$ 513