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Income Taxes - Quarter information (Detail) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Mar. 31, 2020
Jun. 30, 2021
Jun. 30, 2020
Income Taxes          
Effective tax rate of income (loss) before income taxes 22.90% 22.20%   22.80% 19.50%
Excess tax benefits associated with equity-based compensation $ 2 $ 2   $ 11 $ 23
Equity in net losses of unconsolidated entities 11 14   20 40
Increase (decrease) to accruals and related deferred taxes     $ 6    
Tax audit increase (decrease) (1) (5)      
Investments Qualifying for Federal Tax Credits [Member]          
Income Taxes          
Equity in net losses of unconsolidated entities 12 17   21 43
Income tax (expense) benefit, including tax credits, from equity method investment 16 17   32 41
Interest expense $ 3 $ 3   $ 5 6
Refined Coal Facility [Member]          
Income Taxes          
Equity method investments impairment charges     $ 7   $ 7