Employee Benefits (Weighted Average Assumptions- Accrued Postretirement Benefits - Other Postretirement Benefit Plans) (Details) - Other Postretirement Benefit Plan		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Effect of One Percentage Point Increase on Accumulated Postretirement Benefit Obligation, Percentage		14.20%
Defined Benefit Plan, Effect of One Percentage Point Decrease on Accumulated Postretirement Benefit Obligation, Percentage		18.50%
Accrued Postretirement Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate		3.79%	4.36%
Ultimate		4.50%	4.50%
Year ultimate reached	[1]	2026	2026
Defined Benefit Plan, Effect of One Percentage Point Increase on Discount Rate		1.00%
Defined Benefit Plan, Effect of One Percentage Point Decrease on Discount Rate		1.00%
Pre-65 medical | Accrued Postretirement Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Initial		6.25%	6.50%
Post-65 medical | Accrued Postretirement Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Initial		4.50%	4.50%
Pre-65 drug | Accrued Postretirement Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Initial		7.25%	7.50%
Post-65 drug | Accrued Postretirement Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Initial		10.00%	10.50%

[1] Pre-65 medical reaches the ultimate trend rate in 2025. Additionally, the Post-65 medical trend is assumed to be 4.50% for all years into the future.