Quarterly report pursuant to Section 13 or 15(d)

Roll-forward of Common Stock, Additional Paid-in Capital, and Retained Earnings Accounts (Detail)

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Roll-forward of Common Stock, Additional Paid-in Capital, and Retained Earnings Accounts (Detail) (USD $)
In Millions, except Per Share data, unless otherwise specified
 3 Months Ended 12 Months Ended 3 Months Ended 12 Months Ended 3 Months Ended 3 Months Ended
Mar. 31, 2013
Mar. 31, 2013
Mar. 31, 2012
Mar. 31, 2013
Class A common stock
Mar. 31, 2012
Class A common stock
Dec. 31, 2012
Class A common stock
Mar. 31, 2013
Class B common stock
Mar. 31, 2012
Class B common stock
Dec. 31, 2012
Class B common stock
Mar. 31, 2013
Additional Paid-in Capital
Mar. 31, 2012
Additional Paid-in Capital
Dec. 31, 2012
Additional Paid-in Capital
Mar. 31, 2013
Retained Earnings
Mar. 31, 2013
Retained Earnings
Mar. 31, 2012
Retained Earnings
Stockholders Equity Note [Roll Forward]                              
Balance at beginning of period         240 240   725 725            
Common stock purchases (12.2)   (7.1) (2.0) (2.0)   (10.0) (5.0)              
Stock award plans       3 2                    
Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures       $ 0   $ 0                  
Common stock issuances       1 1                    
Conversions of Class A to Class B common stock       (6) (5)   6 5              
Stock Issued During Period, Value, Conversion of Convertible Securities       0   0 0   0            
Balance at end of period       221 236   725 725              
Balance at beginning of period   4,653     3 3   7 7   0 0   7,997 10,128
Stock award plans                   216 210        
Common stock issuances       0   0       70 63        
Option premiums received (paid)                   (100) 155        
Net income 1,037 1,037 970                   1,037   970
Dividends ($0.57 and $0.52 per share)                         (594)   (551)
Common stock purchases (1,013)   (542) (1)   0 0   0 (186) (428)   (826)   (114)
Balance at end of period $ 4,028 $ 4,028   $ 2 $ 3 $ 3 $ 7 $ 7 $ 7 $ 0 $ 0 $ 0 $ 7,614 $ 7,614 $ 10,433
Common stock, cash paid for dividends, per share                           $ 0.62 $ 0.57