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Long-Term Debt (Details Textual) (USD $)
In Millions, unless otherwise specified
1 Months Ended 9 Months Ended 1 Months Ended 9 Months Ended 1 Months Ended
Aug. 04, 2011
Apr. 12, 2010
Sep. 30, 2012
Dec. 31, 2011
Aug. 04, 2011
2016 Notes [Member]
Aug. 04, 2012
2017 Notes [Member]
Sep. 30, 2012
2019 Notes [Member]
Apr. 12, 2010
2020 Notes [Member]
Apr. 12, 2010
2040 Notes [Member]
Aug. 04, 2011
2041 Notes [Member]
Debt Instrument [Line Items]                    
Issuance of unsecured senior notes $ 750 $ 1,000     $ 500 $ 500 $ 750 $ 750 $ 250 $ 250
Unsecured senior debt stated interest rate in %         3.50% 2.30%   6.875% 8.125% 7.00%
Minimum incremental increase in interest rate on the notes             0.25%      
Maximum incremental increase in interest rate on the notes             2.00%      
Long-Term Debt (Textual) [Abstract]                    
Offer to repurchase the notes upon control triggering event     101.00%              
Number of days ceased to be rated investment grade for becoming change of control triggering event     60 days              
Carrying value of the notes     3,116 2,595            
Estimated fair value of the notes     $ 3,545 $ 2,801