Notes Payable and Long-term Debt (Schedule of Notes Payable and Long-term Debt) (Details) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2012
Dec. 31, 2011
Total debt issued and outstanding $ 4,731 $ 4,605
Face 575 Million Notes due 2014 One Point Four Percent [Member]
   
Total debt issued and outstanding 0 573
Interest rate on borrowed funds 1.40%  
Face 400 Million Notes due 2015 1 Point 625 Percent [Member]
   
Total debt issued and outstanding 0 397
Interest rate on borrowed funds 1.625%  
Face 251 Million Debentures due 2018 6 Point 75 Percent [Member]
   
Total debt issued and outstanding 251 251
Interest rate on borrowed funds 6.75%  
Face 340 Million Debentures due 2018 6 Point 40 Percent [Member]
   
Total debt issued and outstanding 338 338
Interest rate on borrowed funds 6.40%  
Face 500 Notes due 2020 4 point 40 Percent [Member]
   
Total debt issued and outstanding 497 496
Interest rate on borrowed funds 4.40%  
Face 1000 Million Notes due 2020 3 Point 125 Percent [Member]
   
Total debt issued and outstanding 991 989
Interest rate on borrowed funds 3.125%  
Face 1,100 Million Notes Due 2022 Two Point Five Zero Five Percent [Member] [Member]
   
Total debt issued and outstanding 1,092 0
Interest rate on borrowed funds 2.50%  
Face 382 Million Debentures due 2027 Seven Point Two Zero Percent [Member]
   
Total debt issued and outstanding 368 367
Interest rate on borrowed funds 7.20%  
Face 185 Million Debentures due 2028 Seven Point Zero Zero Percent [Member]
   
Total debt issued and outstanding 184 184
Interest rate on borrowed funds 7.00%  
Face 600 Million Notes due 2040 Four Point Eight Seven Five Percent [Member]
   
Total debt issued and outstanding 591 591
Interest rate on borrowed funds 4.875%  
Face 425 Million Notes Due 2041 Four Point Seven Percent [Member]
   
Total debt issued and outstanding $ 419 $ 419
Interest rate on borrowed funds 4.70%