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Financial Instruments - Summary of Unrealized Gains (Losses) on Available-for-Sale Investments Recognized in OCI (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Disclosure of detailed information about financial instruments [abstract]    
Mark-to-market (losses) gains on available-for-salesecurities $ (17) $ 86
Deferred income tax expense in OCI   (11)
Unrealized (losses) gains on available-for-sale securities, net of tax (17) 75
Reclassification adjustment for realized gains on disposition of available-for-sale securities recognized in net earnings (loss), net of tax (15) (12)
Gains (losses) on available-for-sale financial assets $ (32) $ 63