Goodwill And Other Intangible Assets (Schedule Of Goodwill) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Corporate Segment [Member]
Goodwill [Line Items]
Goodwill, Beginning Balance	$ 1,014	$ 1,014
Impairment losses	0	0
Goodwill, Ending Balance	1,014	1,014
Zions Bank [Member]
Goodwill [Line Items]
Goodwill, Beginning Balance	20	20
Impairment losses	0	0
Goodwill, Ending Balance	20	20
California Bank Trust [Member]
Goodwill [Line Items]
Goodwill, Beginning Balance	379	379
Impairment losses	0	0
Goodwill, Ending Balance	379	379
Amegy Corporation [Member]
Goodwill [Line Items]
Goodwill, Beginning Balance	615	615
Impairment losses	0	0
Goodwill, Ending Balance	$ 615	$ 615