Quarterly Financial Information (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Litigation charges, after tax	$ 35	$ 40	$ 240	$ 75	$ 118
Charge related to voluntary retirement program, after-tax				$ 47
Charge for refund of amounts from customers, after tax					756
Tax charge related to regulatory assets committed to forgo recovery					198
Regulatory asset impairment charges committed to forgo recovery					264
Charge for utility plant but committed to forgo recovery, after tax					$ 86