| 
           Notional Amounts of Outstanding Derivative Positions (Detail) 
        In Millions, unless otherwise specified  | 
        
           Mar. 31, 2012
 
          CAD 
         | 
        
           Mar. 31, 2012
 
          EUR (€) 
         | 
        
           Mar. 31, 2012
 
          GBP (£) 
         | 
        
           Dec. 31, 2011
 
          CAD 
         | 
        
           Dec. 31, 2011
 
          EUR (€) 
         | 
        
           Dec. 31, 2011
 
          GBP (£) 
         | 
        
           Mar. 31, 2012
 
          Fixed to Floating Interest Rate Swaps
 
          USD ($) 
         | 
        
           Dec. 31, 2011
 
          Fixed to Floating Interest Rate Swaps
 
          USD ($) 
         | 
        
           Mar. 31, 2012
 
          Floating to Fixed Interest Rate Swaps
 
          USD ($) 
         | 
        
           Dec. 31, 2011
 
          Floating to Fixed Interest Rate Swaps
 
          USD ($) 
         | 
        
           Mar. 31, 2012
 
          Basis Interest Rate Swaps
 
          USD ($) 
         | 
        
           Dec. 31, 2011
 
          Basis Interest Rate Swaps
 
          USD ($) 
         | 
        
           Mar. 31, 2012
 
          Forward Starting Swaps
 
          USD ($) 
         | 
        
           Dec. 31, 2011
 
          Forward Starting Swaps
 
          USD ($) 
         | 
      
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Derivative [Line Items] | ||||||||||||||
| Currency Hedges | 474 | € 2,337 | £ 876 | 318 | € 1,685 | £ 870 | ||||||||
| Interest Rate Hedges | $ 6,424 | $ 6,424 | $ 789 | $ 791 | $ 2,500 | $ 0 | $ 500 | $ 0 |