Contingent Liabilities (Narrative) (Details) - USD ($)		12 Months Ended
	Jan. 17, 2014	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Loss Contingencies [Line Items]
Legal fees		$ 15,000,000	$ 19,000,000	$ 21,000,000
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		$ 29,000,000
Butte Local Development v. Masters Group v. Comerica Bank
Loss Contingencies [Line Items]
Amount of damages awarded by the jury	$ 52,000,000