Income Taxes - Additional information (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Taxes
Investment impairment				$ 52.0
Income tax expense at U.S. federal statutory rate		21.00%	21.00%	21.00%
Equity in net losses of unconsolidated entities		$ 36.0	$ 68.0	$ 55.0
Investment tax credit		8.0
Other federal tax credits		5.0	7.0	11.0
Nondeductible acquisition transaction costs			27.0	10.0
Reduction in provision for income taxes due to tax audit settlements		$ 13.0	10.0	2.0
Expected time of completion of IRS audits		15 months
Increase (decrease) to accruals and related deferred taxes		$ 17.0	(3.0)	(22.0)
Reduction in provision for income taxes due to state net operating losses and credits		15.0	12.0	14.0
Excess tax benefits associated with equity-based compensation		18.0	27.0	25.0
Increase (decrease) in provision for income taxes due to impairments				15.0
Investments Qualifying for Federal Tax Credits [Member]
Income Taxes
Equity in net losses of unconsolidated entities		51.0	73.0	46.0
Income tax (expense) benefit, including tax credits, from equity method investment		$ 74.0	87.0	$ 96.0
Refined Coal Facility [Member]
Income Taxes
Equity method investments impairment charges	$ 7.0		$ 7.0