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Retirement Plans (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended 6 Months Ended 12 Months Ended 3 Months Ended 6 Months Ended 3 Months Ended 6 Months Ended 1 Months Ended
Jun. 30, 2011
Jun. 30, 2011
Dec. 31, 2010
Jun. 30, 2011
Pension Benefits [Member]
Jun. 30, 2010
Pension Benefits [Member]
Jun. 30, 2011
Pension Benefits [Member]
Jun. 30, 2010
Pension Benefits [Member]
Jun. 30, 2011
Other Postretirement Benefits [Member]
Jun. 30, 2010
Other Postretirement Benefits [Member]
Jun. 30, 2011
Other Postretirement Benefits [Member]
Jun. 30, 2010
Other Postretirement Benefits [Member]
Jun. 30, 2011
Previous Estimate [Member]
Jun. 30, 2011
Current Estimate [Member]
Jul. 31, 2011
July Contribution [Member]
Service cost       $ 9 $ 8 $ 18 $ 16 $ 1   $ 1        
Interest cost       15 14 30 28   1 1 2      
Expected return on plan assets       (11) (9) (21) (18)              
Amortization of prior service cost       1 1 2 2 (1)   (1)        
Net actuarial loss       8 7 16 14              
Net periodic benefit cost       22 21 45 42   1 1 2      
Estimated qualified pension plan contribution                       84 346  
Qualified pension plan contribution   $ 246                       $ 100
Allocation percentage for equity securities 20.00%   47.50%                      
Allocation percentage for fixed income 70.00%   40.00%                      
Allocation percentage for other investment types 10.00%   12.50%