Contingent Liabilities (Narrative) (Details) - USD ($) |
12 Months Ended | |||
|---|---|---|---|---|
Jan. 17, 2014 |
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| Loss Contingencies [Line Items] | ||||
| Legal fees | $ 17,000,000 | $ 15,000,000 | $ 19,000,000 | |
| 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 | $ 33,000,000 | |||
| Butte Local Development v. Masters Group v. Comerica Bank | ||||
| Loss Contingencies [Line Items] | ||||
| Amount of damages awarded by the jury | $ 52,000,000 | |||