Income tax (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Jun. 30, 2012	Jun. 30, 2011
Income Tax Disclosure [Abstract]
Effective Income Tax Rate	13.40%	12.80%
Unrecognized Tax Benefits	$ 73.3
Unrecognized Tax Benefits, Period Increase (Decrease)	$ 2.7