Employee Benefits Defined benefit plans disclosures (Details)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Total debt securities [Abstract]
Time over which set performance objectives for each investment manager are expected to be met (in years)	3 years
Minimum [Member]
Total debt securities [Abstract]
Average maturities for investment-grade intermediate-term debt (in years)	5 years
Average maturities for investment-grade long-term debt (in years)	10 years
Maximum [Member]
Total debt securities [Abstract]
Average maturities for investment-grade intermediate-term debt (in years)	10 years
Average maturities for below-investment-grade debt (in years)	10 years
Total domestic equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total domestic equity securities (in hundredths)	38.00%	34.00%
Policy Range [Abstract]
Total domestic equity securities - minimum range (in hundredths)	35.00%	35.00%
Total domestic equity securities - maximum range (in hundredths)	45.00%	45.00%
Total foreign securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total domestic equity securities (in hundredths)	25.00%	25.00%
Policy Range [Abstract]
Total domestic equity securities - minimum range (in hundredths)	25.00%	25.00%
Total domestic equity securities - maximum range (in hundredths)	35.00%	35.00%
Developed market foreign equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total domestic equity securities (in hundredths)	20.00%	20.00%
Emerging market foreign equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total domestic equity securities (in hundredths)	5.00%	5.00%
Total debt securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total domestic equity securities (in hundredths)	27.00%	28.00%
Policy Range [Abstract]
Total domestic equity securities - minimum range (in hundredths)	25.00%	25.00%
Total domestic equity securities - maximum range (in hundredths)	35.00%	35.00%
Investment grade intermediate term debt [Member]
Defined Benefit Plan Disclosure [Line Items]
Total domestic equity securities (in hundredths)	7.00%	4.00%
Investment grade long-term debt [Member]
Defined Benefit Plan Disclosure [Line Items]
Total domestic equity securities (in hundredths)	11.00%	14.00%
Below-Investment grade debt [Member]
Defined Benefit Plan Disclosure [Line Items]
Total domestic equity securities (in hundredths)	9.00%	10.00%
Inflation protection securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total domestic equity securities (in hundredths)	9.00%	9.00%
Policy Range [Abstract]
Total domestic equity securities - minimum range (in hundredths)	0.00%	0.00%
Total domestic equity securities - maximum range (in hundredths)	10.00%	10.00%
Cash and short-term investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total domestic equity securities (in hundredths)	1.00%	4.00%
Policy Range [Abstract]
Total domestic equity securities - minimum range (in hundredths)	0.00%	0.00%
Total domestic equity securities - maximum range (in hundredths)	3.00%	3.00%