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Stock-based Compensation Plans - Additional Information (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Aggregate intrinsic value of stock options outstanding $ 64      
Aggregate intrinsic value of stock options exercisable 56      
Total intrinsic value of options exercised 26 $ 45 $ 62  
Total unrecognized compensation cost related to nonvested stock-based compensation arrangements 485      
Expected to be recognized in 2018 246      
Expected to be recognized in 2019 158      
Expected to be recognized in 2020 58      
Expected to be recognized in 2021 22      
Expected to be recognized in 2022 $ 1      
Future Grants Shares 45,000,000      
Employee Stock Option        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Stock option maximum term 10 years      
Stock options vesting period Four or Five Years      
Weighted-average remaining contractual life of stock options exercisable, in years 4 years 3 months 19 days      
Performance Shares        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Performance period to determine shares earned 3 years      
Performance shares outstanding 1,100,000      
Performance Shares | Achievement Exceeds Predefined Target | Maximum        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Performance shares to be awarded as a percentage of total target award 250.00%      
Performance Shares | Achievement Falls Below Threshold        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Performance shares to be awarded 0      
Restricted Stock        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Performance shares to be awarded 2,495,000 1,678,000 1,254,000  
Performance shares outstanding 5,428,000 5,112,000 3,571,000 4,138,000
Restricted stock awards, vesting period 3 years      
DSPP        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Percentage purchase price of stock lower of stock price at beginning or end of plan period at specified intervals 92.50%