Investments - Investments Reported in Other Current and Non-Current Assets (Parenthetical) (Detail) |
12 Months Ended |
|---|---|
|
Dec. 31, 2020
Plant
| |
| Fourteen 2009 Era Clean Coal Plants [Member] | Controlling Interest [Member] | |
| Schedule of Equity Method Investments [Line Items] | |
| Number of coal plants | 14 |
| One 2011 Era Clean Coal Plant [Member] | Noncontrolling Interests [Member] | |
| Schedule of Equity Method Investments [Line Items] | |
| Number of coal plants | 1 |
| Twenty 2011 Era Clean Coal Plants [Member] | Controlling Interest [Member] | |
| Schedule of Equity Method Investments [Line Items] | |
| Number of coal plants | 20 |