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Pension and Postretirement Benefit Plans and Defined Contribution Plans - Healthcare Cost Trend Rate Assumptions (Details) - Postretirement Plans [Member]
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]    
Healthcare cost trend rate assumed for next year (up to age 65) 6.30% 6.50%
Healthcare cost trend rate assumed for next year (age 65 and older) 7.40% 7.90%
Rate to which the cost trend rate is assumed to decline 4.50% 4.50%
Year that the rate reaches the ultimate trend rate 2037 2037