Derivative Instruments (Net Cash Received (Paid) Related to Derivatives) (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| Derivative Instruments and Hedging Activities Disclosure [Abstract] | |||
| Total operating activities | $ 244.4 | $ 6.8 | $ 4.3 |
| Total investing activities | 0.0 | (0.5) | (2.9) |
| Total financing activities | 112.8 | (138.1) | (251.5) |
| Total | $ 357.2 | $ (131.8) | $ (250.1) |