Contingent Liabilities (Narrative) (Details) - USD ($) $ in Millions |
3 Months Ended | ||
|---|---|---|---|
Jan. 17, 2014 |
Mar. 31, 2018 |
Mar. 31, 2017 |
|
| Loss Contingencies [Line Items] | |||
| Legal fees | $ 3 | $ 5 | |
| 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 | $ 28 | ||
| Butte Local Development v. Masters Group v. Comerica Bank | |||
| Loss Contingencies [Line Items] | |||
| Amount of damages awarded by the jury | $ 52 | ||