CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Apr. 30, 2013	Apr. 30, 2012
Operating activities [Abstract]:
Net income	$ 55.6	$ 78.9
Adjustments to reconcile net income to net cash provided by operating activities [Abstract]:
Depreciation and amortization	33.1	29.2
Stock-based compensation expense	33.5	33.4
Excess tax benefits from stock-based compensation	(9.0)	(9.9)
Restructuring benefits	0.4	0
Other Operating Activities, Cash Flow Statement	6.7	(1.1)
Changes in operating assets and liabilities, net of business combinations	103.8	8.8
Net cash provided by operating activities	224.1	139.3
Investing activities [Abstract]:
Purchases of marketable securities	(264.6)	(447.8)
Sales of marketable securities	128.1	48.8
Maturities of marketable securities	68.9	128.5
Capital expenditures	(25.8)	(11.5)
Acquisitions, net of cash acquired	(34.7)	0
Other investing activities	(3.6)	(5.0)
Net cash used in investing activities	(131.7)	(287.0)
Financing activities [Abstract]:
Proceeds from issuance of common stock, net of issuance costs	70.0	153.0
Repurchases of common stock	(129.2)	(99.2)
Excess tax benefits from stock-based compensation	9.0	9.9
Net cash used in financing activities	(50.2)	63.7
Effect of exchange rate changes on cash and cash equivalents	1.4	1.6
Net increase in cash and cash equivalents	43.6	(82.4)
Cash and cash equivalents at beginning of fiscal year	1,612.2	1,156.9
Cash and cash equivalents at end of period	$ 1,655.8	$ 1,074.5