Contingent Liabilities (Narrative) (Details) - USD ($) $ in Millions		3 Months Ended
	Jan. 17, 2014	Mar. 31, 2020	Mar. 31, 2019
Loss Contingencies [Line Items]
Legal fees		$ 2	$ 1
Pending Litigation | Minimum
Loss Contingencies [Line Items]
Loss contingency, estimate of possible loss		0
Pending Litigation | Maximum
Loss Contingencies [Line Items]
Loss contingency, estimate of possible loss		$ 45
Butte Local Development v. Masters Group v. Comerica Bank
Loss Contingencies [Line Items]
Amount of damages awarded by the jury	$ 52