Employee Benefit Plans (Details 2)	12 Months Ended
	Dec. 31, 2014 item	Dec. 31, 2013	Dec. 31, 2012
Weighted-average assumptions used to determine benefit obligations
Discount rate (as a percent)	3.50%	4.90%
Weighted-average assumptions used to determine net periodic benefit costs
Discount rate (as a percent)	4.90%	4.00%
Original discount rate (as a percent)			4.80%
Long-term rate of return on assets (as a percent)	6.00%	6.00%	6.50%
Guidelines regarding allocation of assets
Number of companies or government agencies in which the allocation of assets should not exceed 10% of the total fund	1
Maximum allocation of assets in the securities of any one company or government agency (as a percent)	10.00%
Maximum allocation of assets in any one industry (as a percent)	20.00%
Number of industries in which the allocation of assets should be no more than 20% of the total fund	1
Individual treasury securities (as a percent)	50.00%
Treasury bonds and notes, maximum (as a percent)	100.00%
Employee Benefit Plans
Total (as a percent)	100.00%	100.00%
Equity securities
Employee Benefit Plans
Total (as a percent)	4.20%	9.40%
Debt securities
Employee Benefit Plans
Total (as a percent)	94.00%	85.10%
Other investments
Employee Benefit Plans
Total (as a percent)	1.80%	5.50%
Fixed income securities
Employee Benefit Plans
Total (as a percent)	95.00%
Equity securities and other investments
Employee Benefit Plans
Total (as a percent)	5.00%