Financial Instruments (Realized Gains and Losses) (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||
---|---|---|---|---|
Jun. 30, 2019 |
Jun. 30, 2018 |
Jun. 30, 2019 |
Jun. 30, 2018 |
|
Fair Value Disclosures [Abstract] | ||||
Proceeds from sales | $ 362.9 | $ 4,953.8 | $ 456.6 | $ 5,546.4 |
Realized gross gains on sales | 13.0 | 5.6 | 15.5 | 7.7 |
Realized gross losses on sales | $ 6.4 | $ 47.4 | $ 6.8 | $ 49.0 |