Investment in Cenovus Energy (Schedule of Investment in Common Shares Carried at Fair Value) (Details) - Cenovus Energy Inc [Member] - USD ($) $ / shares in Units, shares in Millions, $ in Millions |
Dec. 31, 2021 |
Dec. 31, 2020 |
|---|---|---|
| Debt and Equity Securities, FV-NI [Line Items] | ||
| Number of shares of CVE common stock (millions) | 91 | 208 |
| Ownership of issued and outstanding common stock | 4.50% | 16.90% |
| Closing price on NYSE on last trading day ($/share) | $ 12.28 | $ 6.04 |
| Fair Value (millions of dollars) | $ 1,117 | $ 1,256 |