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Postretirement Benefit Plans (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2012
Mar. 31, 2011
Net periodic benefit cost    
Service cost $ 2 $ 2
Interest cost 5 6
Expected return on plan assets (4) (5)
Amortization of net actuarial loss 3 2
Net periodic benefit cost (income) 6 5
Pension [Member]
    
Net periodic benefit cost    
Service cost 2 1
Interest cost 3 4
Expected return on plan assets (4) (5)
Amortization of net actuarial loss 2 1
Net periodic benefit cost (income) 3 1
Other Benefits [Member]
    
Net periodic benefit cost    
Service cost 0 1
Interest cost 2 2
Expected return on plan assets 0 0
Amortization of net actuarial loss 1 1
Net periodic benefit cost (income) $ 3 $ 4