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Income Taxes - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended 12 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Income Tax Disclosure [Abstract]      
Federal statutory income tax rate 21.00%   35.00%
Income tax benefit related to revaluation of net deferred tax liability $ 242    
Effective income tax rate (4.80%) 9.80%