Employee Benefit Plans (Details 2)	12 Months Ended
	Dec. 31, 2012 item	Dec. 31, 2011	Dec. 31, 2010
Weighted-average assumptions used to determine benefit obligations
Discount rate (as a percent)	4.00%	4.80%
Weighted-average assumptions used to determine net periodic benefit costs
Discount rate (as a percent)	4.80%	4.70%	6.00%
Original discount rate (as a percent)		5.50%
Long-term rate of return on assets (as a percent)	6.50%	7.75%	8.50%
Rate of compensation increase (as a percent)			4.00%
Guidelines regarding allocation of assets
Allocation target in 2012, minimum (as a percent)	90.00%
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)	9.60%	13.40%
Debt securities
Employee Benefit Plans
Total (as a percent)	85.30%	77.40%
Other investments
Employee Benefit Plans
Total (as a percent)	5.10%	9.20%
Fixed income securities
Employee Benefit Plans
Total (as a percent)	85.00%
Equity securities and other investments
Employee Benefit Plans
Total (as a percent)	15.00%