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Stock-Based Compensation - Schedule of Reduction in Stated Value of Company's Common Shares (Detail) (USD $)
In Millions, except Share data, unless otherwise specified
 12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]      
Number of shares, Awarded and not released, Beginning balance 882,988 1,026,304 1,182,736
Number of shares, Release of restricted stock (152,512) (143,316) (156,432)
Number of shares, Awarded and not released, Ending balance 730,476 882,988 1,026,304
Stated value, Awarded and not released, Beginning balance $ 30 $ 35 $ 40
Stated value, Release of restricted stock (5) (5) (5)
Stated value, Awarded and not released, Ending balance $ 25 $ 30 $ 35