Investment in Cenovus Energy - Gains and Losses Recorded in Other Income (Loss) (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2021 |
Jun. 30, 2020 |
Jun. 30, 2021 |
Jun. 30, 2020 |
|
| Debt and Equity Securities, FV-NI [Line Items] | ||||
| Total net gain (loss) on equity securities | $ 726.0 | $ (1,140.0) | ||
| Cenovus Energy Inc [Member] | ||||
| Debt and Equity Securities, FV-NI [Line Items] | ||||
| Total net gain (loss) on equity securities | $ 418.0 | $ 551.0 | 726.0 | (1,140.0) |
| Less: Net gain on equity securities sold during the period | 31.0 | 0.0 | 60.0 | 0.0 |
| Unrealized gain (loss) on equity securities still held at the reporting date | $ 387.0 | $ 551.0 | $ 666.0 | $ (1,140.0) |