Employee Benefit Plans - Assumptions in Benefit Plans (Details) - Postretirement Benefits Other than Pensions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Weighted-average assumptions used to determine projected pension benefit obligations
Discount rate (as a percent)	4.30%	4.25%	4.00%
Discount rate beginning of year (as a percent)	4.25%	4.00%	4.75%
Pre 65
Weighted-average assumptions used to determine projected pension benefit obligations
Health care cost trend rate for medical benefits assumed for next year (as a percent)	7.50%	5.50%	6.00%
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate) (as a percent)	4.50%	4.50%	4.50%
Year that the rate reaches the ultimate trend rate (pre-65)	2023	2018	2018
Post 65
Weighted-average assumptions used to determine projected pension benefit obligations
Health care cost trend rate for medical benefits assumed for next year (as a percent)	5.00%	5.50%	6.00%
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate) (as a percent)	4.50%	4.50%	4.50%
Year that the rate reaches the ultimate trend rate (pre-65)	2018	2018	2018