Subsequent Events (Narrative) (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
	Oct. 10, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Subsequent Event [Line Items]
Operation, maintenance and other		$ 1,584	$ 1,476	$ 4,592	$ 4,385
Hurricane Michael Storm Damage [Member] | Estimated Impact [Member]
Subsequent Event [Line Items]
Operation, maintenance and other	$ 235
Estimated capital cost	$ 185