Annual report pursuant to Section 13 and 15(d)

Postretirement Benefits Postretirement Benefits - Additional Information (Details)

v3.6.0.2
Postretirement Benefits Postretirement Benefits - Additional Information (Details)
 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Defined Benefit Plan, Assumed Health Care Cost Trend Rates [Abstract]      
Health Care Cost Trend Rate for Next Year 5.70% 5.80%  
Rate to Which the Cost Trend Rate is Assumed to Decline (the Ultimate Trend Rate) 4.50% 4.50%  
Year Rate Reaches the Ultimate Trend Rate 2037 2037  
Defined Benefit Plan, Actual Plan Asset Allocations [Abstract]      
Total 100.00% 100.00%  
Defined Benefit Plan, Assets, Target Allocations [Abstract]      
Total 100.00%    
Pension Plans [Member]      
Defined Benefit Plan, Weighted average assumptions used to determine pension and other postretirement benefit obligations [Abstract]      
Discount Rate 4.00% 4.40%  
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]      
Discount Rate 3.58% 3.95% 4.85%
Long-Term Rate of Return on Plan Assets 5.25% 6.00% 6.25%
Other Postretirement Benefit Plans [Member]      
Defined Benefit Plan, Weighted average assumptions used to determine pension and other postretirement benefit obligations [Abstract]      
Discount Rate 3.93% 4.23%  
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]      
Discount Rate 3.30% 3.75% 4.40%
United States Equity Securities [Member]      
Defined Benefit Plan, Actual Plan Asset Allocations [Abstract]      
Total 19.00% 17.00%  
Defined Benefit Plan, Assets, Target Allocations [Abstract]      
Total 17.00%    
International Equity Securities [Member]      
Defined Benefit Plan, Actual Plan Asset Allocations [Abstract]      
Total 3.00% 3.00%  
Defined Benefit Plan, Assets, Target Allocations [Abstract]      
Total 3.00%    
Fixed Income Securities [Member]      
Defined Benefit Plan, Actual Plan Asset Allocations [Abstract]      
Total 75.00% 77.00%  
Defined Benefit Plan, Assets, Target Allocations [Abstract]      
Total 80.00%    
Short-Term Investments [Member]      
Defined Benefit Plan, Actual Plan Asset Allocations [Abstract]      
Total 3.00% 3.00%  
Defined Benefit Plan, Assets, Target Allocations [Abstract]      
Total 0.00%