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Investments (Distribution Of Securities By Percentage Of Fair Value Below Book Value By More Than 5%) (Detail) (USD $)
In Millions, unless otherwise specified
Sep. 30, 2013
Dec. 31, 2012
Available For Sale Securities [Abstract]    
Fixed-maturity securities held as available-for-sale, amortized cost $ 6,443 $ 6,122
Available For Sale Securities 6,377 6,221
Held To Maturity Securities [Abstract]    
Held-To-Maturity Securities Amortized Cost 2,809 2,829
Held-To-Maturity Securities Fair Value 2,566 2,674
> 5% To 15% [Member]
    
Held To Maturity Securities [Abstract]    
Percentage Of Fair Value Below Book Value Minimum 5.00%  
Percentage Of Fair Value Below Book Value Maximum 15.00%  
> 5% To 15% [Member] | Unrealized loss position > 12 months
    
Available For Sale Securities [Abstract]    
Number of available-for-sale securities in unrealized loss position 13  
Fixed-maturity securities held as available-for-sale, amortized cost 110  
Available For Sale Securities 101  
Held To Maturity Securities [Abstract]    
Number of Held-To-Maturity Securities in unrealized loss position 0  
Held-To-Maturity Securities Amortized Cost 0  
Held-To-Maturity Securities Fair Value 0  
> 15% To 25% [Member]
    
Held To Maturity Securities [Abstract]    
Percentage Of Fair Value Below Book Value Minimum 15.00%  
Percentage Of Fair Value Below Book Value Maximum 25.00%  
> 15% To 25% [Member] | Unrealized loss position > 12 months
    
Available For Sale Securities [Abstract]    
Number of available-for-sale securities in unrealized loss position 12  
Fixed-maturity securities held as available-for-sale, amortized cost 66  
Available For Sale Securities 52  
Held To Maturity Securities [Abstract]    
Number of Held-To-Maturity Securities in unrealized loss position 0  
Held-To-Maturity Securities Amortized Cost 0  
Held-To-Maturity Securities Fair Value 0  
> 25% To 50% [Member]
    
Held To Maturity Securities [Abstract]    
Percentage Of Fair Value Below Book Value Minimum 25.00%  
Percentage Of Fair Value Below Book Value Maximum 50.00%  
> 25% To 50% [Member] | Unrealized loss position > 12 months
    
Available For Sale Securities [Abstract]    
Number of available-for-sale securities in unrealized loss position 5  
Fixed-maturity securities held as available-for-sale, amortized cost 53  
Available For Sale Securities 36  
Held To Maturity Securities [Abstract]    
Number of Held-To-Maturity Securities in unrealized loss position 1  
Held-To-Maturity Securities Amortized Cost 575  
Held-To-Maturity Securities Fair Value 345  
> 50% [Member]
    
Held To Maturity Securities [Abstract]    
Percentage Of Fair Value Below Book Value Minimum 50.00%  
> 50% [Member] | Unrealized loss position > 12 months
    
Available For Sale Securities [Abstract]    
Number of available-for-sale securities in unrealized loss position 8  
Fixed-maturity securities held as available-for-sale, amortized cost 52  
Available For Sale Securities 9  
Held To Maturity Securities [Abstract]    
Number of Held-To-Maturity Securities in unrealized loss position 0  
Held-To-Maturity Securities Amortized Cost 0  
Held-To-Maturity Securities Fair Value 0  
Greater Than 5% [Member] | Unrealized loss position > 12 months
    
Available For Sale Securities [Abstract]    
Number of available-for-sale securities in unrealized loss position 38  
Fixed-maturity securities held as available-for-sale, amortized cost 281  
Available For Sale Securities 198  
Held To Maturity Securities [Abstract]    
Number of Held-To-Maturity Securities in unrealized loss position 1  
Held-To-Maturity Securities Amortized Cost 575  
Held-To-Maturity Securities Fair Value $ 345