Summary of significant accounting policies Goodwill (Details)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Goodwill
Operating cash flows forecast period assumed in goodwill impairment analysis (in years)	5 years
Minimum period for which terminal value is included from the balance sheet date for goodwill impairment analysis (in years)	5 years
Minimum
Goodwill
Terminal growth rate assumed in goodwill impairment analysis (as a percent)	3.40%	3.00%
Discount rate, pre-tax, used in goodwill impairment analysis (as a percent)	9.60%	9.20%
Maximum
Goodwill
Terminal growth rate assumed in goodwill impairment analysis (as a percent)	5.40%	5.90%
Discount rate, pre-tax, used in goodwill impairment analysis (as a percent)	16.40%	16.50%