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Stock-Based Compensation - Schedule of Reduction in Stated Value of Company's Common Shares (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]    
Number of shares, Awarded and not released, Beginning balance 1,174,648 1,460,952
Number of shares, Release of restricted stock (286,312) (286,304)
Number of shares, Awarded and not released, Ending balance 888,336 1,174,648
Stated value, Awarded and not released, Beginning balance $ 20 $ 25
Stated value, Release of restricted stock (4) (5)
Stated value, Awarded and not released, Ending balance $ 16 $ 20