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Benefit Plans and Other Postretirement Benefits, Expected long-term rate of return (Details) - Pension Benefits - U.S.
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Defined Benefit Plan Disclosure      
Historical compounded return on plan assets (as a percent) 8.75%    
Expected long-term return on assets (as a percent) 7.75% 7.75% 8.00%
Equity securities      
Defined Benefit Plan Disclosure      
Target allocation (as a percent) 60.00%    
Plan asset allocations, assumptions (as a percent) 60.00%    
Equity securities | Minimum      
Defined Benefit Plan Disclosure      
Expected long-term return on assets (as a percent) 8.00%    
Equity securities | Maximum      
Defined Benefit Plan Disclosure      
Expected long-term return on assets (as a percent) 9.00%    
Fixed income securities      
Defined Benefit Plan Disclosure      
Target allocation (as a percent) 40.00%    
Plan asset allocations, assumptions (as a percent) 40.00%    
Fixed income securities | Minimum      
Defined Benefit Plan Disclosure      
Expected long-term return on assets (as a percent) 5.00%    
Fixed income securities | Maximum      
Defined Benefit Plan Disclosure      
Expected long-term return on assets (as a percent) 6.00%