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Pension Plans and Other Postretirement Benefits (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Pension Plans and Other Postretirement Benefits      
Employer's contributions under defined contribution plans $ 187 $ 186 $ 173
Other Postretirement Benefits
     
Defined benefit plan      
Benefit obligation 17 17  
Net periodic benefit cost 1 1 1
Actual plan asset allocations      
Total Company contributions to multiemployer pension plans 47 46 47
Pension Plans
     
Defined benefit plan      
Number of defined benefit plans 9    
Benefit obligation 685 659  
Fair value of plan assets 463 426  
Actual return on plan assets 37 45  
Net periodic benefit cost 49 36 16
Settlements losses included in net periodic costs 25 12  
Weighted-average assumptions used to determine net periodic cost      
Discount rate (as a percent) 4.75% 5.50%  
Expected long-term rate of return on plan assets (as a percent) 7.25% 7.25% 8.50%
Target plan asset allocations      
Equity securities target allocation (as a percent)   50.00% 60.00%
Debt securities target allocation (as a percent)   50.00% 40.00%
Actual plan asset allocations      
Equity securities (as a percent) 47.00% 57.00%  
Debt securities (as a percent) 51.00% 42.00%  
Money market securities (as a percent) 2.00% 1.00%  
Employer's contributions under defined benefit plans 92 65 50
Estimated future employer contributions in next fiscal year 34    
Total Company contributions to multiemployer pension plans $ 11 $ 12 $ 10
Pension Plans | Level 1
     
Actual plan asset allocations      
Actual plan assets (as a percent) 82.00% 71.00%  
Pension Plans | Level 2
     
Actual plan asset allocations      
Actual plan assets (as a percent) 18.00% 29.00%  
Tax-qualified funded pension plans
     
Defined benefit plan      
Number of defined benefit plans 3    
Unfunded nonqualified supplemental retirement plans
     
Defined benefit plan      
Number of defined benefit plans 6    
Number of defined benefit plans not frozen in prior periods 1