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Investments (Fair Values And Gross Unrealized Losses By Credit Rating Category Of Corporate Obligations) (Detail) (USD $)
In Millions, unless otherwise specified
Sep. 30, 2012
Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]    
Total Fair Value $ 1,025 $ 2,387
Total Unrealized Loss (191) (478)
Corporate Obligations [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Total Fair Value 163  
Total Unrealized Loss (28)  
Aa [Member] | Corporate Obligations [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Total Fair Value 4  
A [Member] | Corporate Obligations [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Total Fair Value 74  
Total Unrealized Loss (6)  
Baa [Member] | Corporate Obligations [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Total Fair Value 59  
Total Unrealized Loss (7)  
Below Investment Grade [Member] | Corporate Obligations [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Total Fair Value 14  
Total Unrealized Loss (3)  
Not Rated [Member] | Corporate Obligations [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Total Fair Value 12  
Total Unrealized Loss $ (12)