Employee Benefit Plans - Health Care Cost Trend Rates (Details) - Other Post-retirement Benefits	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Ultimate year trend rate	4.50%	5.00%
Age under 65
Defined Benefit Plan Disclosure [Line Items]
Assumed current trend rate for next year for participants under 65	6.62%	6.80%
Age 65 and over
Defined Benefit Plan Disclosure [Line Items]
Assumed current trend rate for next year for participants 65 and over	7.73%	7.85%