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Income Taxes - Additional Information (Details) - USD ($)
$ in Millions
3 Months Ended 12 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Mar. 31, 2020
Income tax expense $ 20 $ 48  
Effective income tax rate 17.00% 31.00%  
Release of valuation allowance $ 22    
Other adjustments, state law changes $ 6    
Effective income tax rate, excluding effects of special items 31.00%    
US federal statutory income tax rate 21.00%    
Maximum [Member] | Scenario, Forecast [Member]      
Possible release of valuation allowance     $ 86