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Postretirement Benefit Plans (Details 10)
12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Actual versus the expected long-term returns for postretirement plans      
Expected rate of return on plan assets 9.00% 9.00% 9.00%
Actual rate of return on plan assets (3.20%) 14.10% 24.10%