Financial Derivatives (Narrative) (Details) - USD ($) $ in Millions |
3 Months Ended | 12 Months Ended |
|---|---|---|
Mar. 31, 2019 |
Dec. 31, 2018 |
|
| Derivative [Line Items] | ||
| Written credit derivative spread threshold | 20.00% | 20.00% |
| Credit Default Swap, Selling Protection [Member] | ||
| Derivative [Line Items] | ||
| Credit risk derivative in excess of threshold, at fair value, net | $ (0.2) | $ (1.0) |
| Total net up-front payments received | $ (2.0) | $ (2.0) |
| Minimum | ||
| Derivative [Line Items] | ||
| Spread on written credit derivatives | 0.426% | 0.218% |
| Upfront points on written credit derivative in excess of threshold | 36.9 | 56.3 |
| Maximum | ||
| Derivative [Line Items] | ||
| Spread on written credit derivatives | 8.151% | 19.56% |
| Upfront points on written credit derivative in excess of threshold | 75.2 | 74.7 |