Accumulated other comprehensive income (loss) - Changes in Accumulated OCI by Component and Reclassifications Out of Accumulated OCI (Details) $ in Millions	3 Months Ended
	Apr. 30, 2016 USD ($)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	$ 3,060.7
Balance	3,098.2
Foreign currency translation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	(237.8)
Other comprehensive income (loss) (OCI) before reclassifications	30.8
Amounts reclassified from AOCI to net income	0.0
Total other comprehensive (loss) income	30.8
Balance	(207.0)
Losses on available-for-sale securities, net
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	(0.4)
Other comprehensive income (loss) (OCI) before reclassifications	0.2
Amounts reclassified from AOCI to net income	0.0
Total other comprehensive (loss) income	0.2
Balance	(0.2)
Gains (losses) on cash flow hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	(3.9)
Other comprehensive income (loss) (OCI) before reclassifications	3.6
Amounts reclassified from AOCI to net income	1.1
Total other comprehensive (loss) income	4.7
Balance	0.8
Accumulated other comprehensive (loss) income
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	(274.1)
Other comprehensive income (loss) (OCI) before reclassifications	34.6
Amounts reclassified from AOCI to net income	1.0
Total other comprehensive (loss) income	35.6
Balance	(238.5)
Pension Plan | Actuarial losses
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	(43.1)
Other comprehensive income (loss) (OCI) before reclassifications	0.0
Amounts reclassified from AOCI to net income	0.3
Total other comprehensive (loss) income	0.3
Balance	(42.8)
Pension Plan | Prior service credits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance	11.1
Other comprehensive income (loss) (OCI) before reclassifications	0.0
Amounts reclassified from AOCI to net income	(0.4)
Total other comprehensive (loss) income	(0.4)
Balance	$ 10.7