Employee Postretirement Benefits (Weighted-Average Assumptions) (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Pension Plans
Net cost, Discount rate		3.91%	3.86%	4.66%
Net cost, Expected long-term return on plan assets		4.84%	5.21%	5.98%
Net cost, Rate of compensation increase		2.32%	2.63%	2.67%
Benefit obligations, Discount rate		3.19%	3.91%
Benefit obligations, Rate of compensation increase		2.29%	2.32%
Defined Benefit Pension Plans | Scenario, Forecast
Net cost, Discount rate	3.19%
Net cost, Expected long-term return on plan assets	4.46%
Net cost, Rate of compensation increase	2.29%
Other Postretirement Benefit Plans
Net cost, Discount rate		4.59%	4.28%	4.97%
Net cost, Expected long-term return on plan assets		0.00%	0.00%	0.00%
Net cost, Rate of compensation increase		0.00%	0.00%	0.00%
Benefit obligations, Discount rate		4.29%	4.59%
Benefit obligations, Rate of compensation increase		0.00%	0.00%