Financial Instruments Cost and Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Jul. 31, 2017	Jan. 31, 2017	Jul. 31, 2016	Jan. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents	$ 1,174.1	$ 1,213.1	$ 1,467.3	$ 1,353.0
Derivative contract assets, Amortized Cost	3.0	2.2
Derivative contract assets, Gross unrealized gains	10.2	12.3
Derivative contract assets, Gross unrealized losses	(2.2)	(1.3)
Derivative contract assets	11.0	13.2
Derivative contract liabilities, Amortized Cost	0.0	0.0
Derivative contract liabilities, Gross unrealized gains	0.0	0.0
Derivative contract liabilities, Gross unrealized losses	(19.3)	(10.4)
Derivative contract liabilities	(19.3)	(10.4)
Amortized Cost	1,547.4	1,903.5
Gross unrealized gains	19.8	17.4
Gross unrealized losses	(24.7)	(13.6)
Fair Value	1,542.5	1,907.3
Marketable Securities, Current
Schedule of Available-for-sale Securities [Line Items]
Mutual funds, Amortized Cost	48.7	44.8
Mutual funds, Gross unrealized gains	5.7	2.5
Mutual funds, Gross unrealized losses	0.0	0.0
Mutual funds, Fair Value	54.4	47.3
Marketable Securities, Current | Agency bonds
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Amortized Cost	7.5	13.2
Marketable securities, Gross unrealized gains	0.0	0.0
Marketable securities, Gross unrealized losses	0.0
Marketable securities, Fair Value	7.5	13.2
Marketable Securities, Current | Asset backed securities
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Amortized Cost	30.2	19.6
Marketable securities, Gross unrealized gains	0.0	0.0
Marketable securities, Gross unrealized losses	0.0	0.0
Marketable securities, Fair Value	30.2	19.6
Marketable Securities, Current | Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Amortized Cost	13.0	157.3
Marketable securities, Gross unrealized gains	0.0	0.0
Marketable securities, Gross unrealized losses	0.0	0.0
Marketable securities, Fair Value	13.0	157.3
Marketable Securities, Current | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Amortized Cost	98.9	109.2
Marketable securities, Gross unrealized gains	0.0	0.0
Marketable securities, Gross unrealized losses	0.0	0.0
Marketable securities, Fair Value	98.9	109.2
Marketable Securities, Current | Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Amortized Cost	219.3	234.7
Marketable securities, Gross unrealized gains	0.1	0.0
Marketable securities, Gross unrealized losses	0.0	(0.2)
Marketable securities, Fair Value	219.4	234.5
Marketable Securities, Current | Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Amortized Cost	36.7	43.4
Marketable securities, Gross unrealized gains	0.1	0.0
Marketable securities, Gross unrealized losses	0.0	0.0
Marketable securities, Fair Value	36.8	43.4
Marketable Securities, Current | Sovereign debt
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Amortized Cost	14.0	30.0
Marketable securities, Gross unrealized gains	0.0	0.0
Marketable securities, Gross unrealized losses	0.0	0.0
Marketable securities, Fair Value	14.0	30.0
Marketable Securities, Current | U.S. government securities
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Amortized Cost	59.4	32.3
Marketable securities, Gross unrealized gains	0.0	0.0
Marketable securities, Gross unrealized losses	0.0	0.0
Marketable securities, Fair Value	59.4	32.3
Marketable Securities, Noncurrent | Agency bonds
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Amortized Cost	7.5	7.1
Marketable securities, Gross unrealized gains	0.0	0.0
Marketable securities, Gross unrealized losses	0.0	0.0
Marketable securities, Fair Value	7.5	7.1
Marketable Securities, Noncurrent | Asset backed securities
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Amortized Cost	57.6	65.8
Marketable securities, Gross unrealized gains	0.0	0.1
Marketable securities, Gross unrealized losses	(0.1)	0.0
Marketable securities, Fair Value	57.5	65.9
Marketable Securities, Noncurrent | Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Amortized Cost	126.3	172.1
Marketable securities, Gross unrealized gains	0.3	0.1
Marketable securities, Gross unrealized losses	0.0	(0.1)
Marketable securities, Fair Value	126.6	172.1
Marketable Securities, Noncurrent | Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Amortized Cost	5.0	10.7
Marketable securities, Gross unrealized gains	0.0	0.0
Marketable securities, Gross unrealized losses	0.0	0.0
Marketable securities, Fair Value	5.0	10.7
Marketable Securities, Noncurrent | Sovereign debt
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Amortized Cost	1.6	1.5
Marketable securities, Gross unrealized gains	0.0	0.0
Marketable securities, Gross unrealized losses	0.0	0.0
Marketable securities, Fair Value	1.6	1.5
Marketable Securities, Noncurrent | U.S. government securities
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Amortized Cost	37.8	48.8
Marketable securities, Gross unrealized gains	0.0	0.1
Marketable securities, Gross unrealized losses	0.0	0.0
Marketable securities, Fair Value	37.8	48.9
Convertible debt securities
Schedule of Available-for-sale Securities [Line Items]
Convertible debt securities, Amortized Cost	10.7	4.9
Convertible debt securities, Gross unrealized gains	3.4	2.3
Convertible debt securities, Gross unrealized losses	(3.1)	(1.6)
Convertible debt securities, Fair Value	11.0	5.6
Agency bonds
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents	7.0	6.0
Cash equivalents, Fair Value	7.0	6.0
Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents	61.3	63.1
Cash equivalents, Fair Value	61.3	63.1
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents	23.0	40.2
Cash equivalents, Fair Value	23.0	40.2
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents	167.6	207.4
Cash equivalents, Fair Value	167.6	207.4
Custody cash deposit
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents	42.8	3.2
Cash equivalents, Fair Value	42.8	3.2
Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents	15.0	5.0
Cash equivalents, Fair Value	15.0	5.0
Money Market funds
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents	348.5	256.5
Cash equivalents, Fair Value	348.5	256.5
Sovereign debt
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents	5.0	15.0
Cash equivalents, Fair Value	5.0	15.0
U.S. government securities
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents	100.0	309.5
Cash equivalents, Fair Value	100.0	309.5
Level 1
Schedule of Available-for-sale Securities [Line Items]
Derivative contract assets	0.0	0.0
Derivative contract liabilities	0.0	0.0
Fair Value	816.5	1,193.8
Level 1 | Marketable Securities, Current
Schedule of Available-for-sale Securities [Line Items]
Mutual funds, Fair Value	54.4	47.3
Level 1 | Marketable Securities, Current | Agency bonds
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	7.5	13.2
Level 1 | Marketable Securities, Current | Asset backed securities
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	0.0	0.0
Level 1 | Marketable Securities, Current | Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	13.0	157.3
Level 1 | Marketable Securities, Current | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	0.0	0.0
Level 1 | Marketable Securities, Current | Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	219.4	234.5
Level 1 | Marketable Securities, Current | Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	36.8	43.4
Level 1 | Marketable Securities, Current | Sovereign debt
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	0.0	0.0
Level 1 | Marketable Securities, Current | U.S. government securities
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	59.4	32.3
Level 1 | Marketable Securities, Noncurrent | Agency bonds
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	7.5	7.1
Level 1 | Marketable Securities, Noncurrent | Asset backed securities
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	0.0	0.0
Level 1 | Marketable Securities, Noncurrent | Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	126.6	172.1
Level 1 | Marketable Securities, Noncurrent | Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	5.0	10.7
Level 1 | Marketable Securities, Noncurrent | Sovereign debt
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	0.0	0.0
Level 1 | Marketable Securities, Noncurrent | U.S. government securities
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	37.8	48.9
Level 1 | Convertible debt securities
Schedule of Available-for-sale Securities [Line Items]
Convertible debt securities, Fair Value	0.0	0.0
Level 1 | Agency bonds
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents, Fair Value	7.0	6.0
Level 1 | Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents, Fair Value	61.3	63.1
Level 1 | Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents, Fair Value	23.0	40.2
Level 1 | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents, Fair Value	0.0	0.0
Level 1 | Custody cash deposit
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents, Fair Value	42.8	3.2
Level 1 | Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents, Fair Value	15.0	5.0
Level 1 | Money Market funds
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents, Fair Value	0.0	0.0
Level 1 | Sovereign debt
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents, Fair Value	0.0	0.0
Level 1 | U.S. government securities
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents, Fair Value	100.0	309.5
Level 2
Schedule of Available-for-sale Securities [Line Items]
Derivative contract assets	9.0	11.9
Derivative contract liabilities	(19.3)	(10.4)
Fair Value	713.0	706.6
Level 2 | Marketable Securities, Current
Schedule of Available-for-sale Securities [Line Items]
Mutual funds, Fair Value	0.0	0.0
Level 2 | Marketable Securities, Current | Agency bonds
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	0.0	0.0
Level 2 | Marketable Securities, Current | Asset backed securities
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	30.2	19.6
Level 2 | Marketable Securities, Current | Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	0.0	0.0
Level 2 | Marketable Securities, Current | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	98.9	109.2
Level 2 | Marketable Securities, Current | Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	0.0	0.0
Level 2 | Marketable Securities, Current | Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	0.0	0.0
Level 2 | Marketable Securities, Current | Sovereign debt
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	14.0	30.0
Level 2 | Marketable Securities, Current | U.S. government securities
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	0.0	0.0
Level 2 | Marketable Securities, Noncurrent | Agency bonds
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	0.0	0.0
Level 2 | Marketable Securities, Noncurrent | Asset backed securities
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	57.5	65.9
Level 2 | Marketable Securities, Noncurrent | Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	0.0	0.0
Level 2 | Marketable Securities, Noncurrent | Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	0.0	0.0
Level 2 | Marketable Securities, Noncurrent | Sovereign debt
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	1.6	1.5
Level 2 | Marketable Securities, Noncurrent | U.S. government securities
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	0.0	0.0
Level 2 | Convertible debt securities
Schedule of Available-for-sale Securities [Line Items]
Convertible debt securities, Fair Value	0.0	0.0
Level 2 | Agency bonds
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents, Fair Value	0.0	0.0
Level 2 | Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents, Fair Value	0.0	0.0
Level 2 | Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents, Fair Value	0.0	0.0
Level 2 | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents, Fair Value	167.6	207.4
Level 2 | Custody cash deposit
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents, Fair Value	0.0	0.0
Level 2 | Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents, Fair Value	0.0	0.0
Level 2 | Money Market funds
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents, Fair Value	348.5	256.5
Level 2 | Sovereign debt
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents, Fair Value	5.0	15.0
Level 2 | U.S. government securities
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents, Fair Value	0.0	0.0
Level 3
Schedule of Available-for-sale Securities [Line Items]
Derivative contract assets	2.0	1.3
Derivative contract liabilities	0.0	0.0
Fair Value	13.0	6.9
Level 3 | Marketable Securities, Current
Schedule of Available-for-sale Securities [Line Items]
Mutual funds, Fair Value	0.0	0.0
Level 3 | Marketable Securities, Current | Agency bonds
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	0.0	0.0
Level 3 | Marketable Securities, Current | Asset backed securities
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	0.0	0.0
Level 3 | Marketable Securities, Current | Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	0.0	0.0
Level 3 | Marketable Securities, Current | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	0.0	0.0
Level 3 | Marketable Securities, Current | Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	0.0	0.0
Level 3 | Marketable Securities, Current | Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	0.0	0.0
Level 3 | Marketable Securities, Current | Sovereign debt
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	0.0	0.0
Level 3 | Marketable Securities, Current | U.S. government securities
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	0.0	0.0
Level 3 | Marketable Securities, Noncurrent | Agency bonds
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	0.0	0.0
Level 3 | Marketable Securities, Noncurrent | Asset backed securities
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	0.0	0.0
Level 3 | Marketable Securities, Noncurrent | Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	0.0	0.0
Level 3 | Marketable Securities, Noncurrent | Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	0.0	0.0
Level 3 | Marketable Securities, Noncurrent | Sovereign debt
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	0.0	0.0
Level 3 | Marketable Securities, Noncurrent | U.S. government securities
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value	0.0	0.0
Level 3 | Convertible debt securities
Schedule of Available-for-sale Securities [Line Items]
Convertible debt securities, Fair Value	11.0	5.6
Level 3 | Agency bonds
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents, Fair Value	0.0	0.0
Level 3 | Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents, Fair Value	0.0	0.0
Level 3 | Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents, Fair Value	0.0	0.0
Level 3 | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents, Fair Value	0.0	0.0
Level 3 | Custody cash deposit
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents, Fair Value	0.0	0.0
Level 3 | Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents, Fair Value	0.0	0.0
Level 3 | Money Market funds
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents, Fair Value	0.0	0.0
Level 3 | Sovereign debt
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents, Fair Value	0.0	0.0
Level 3 | U.S. government securities
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents, Fair Value	$ 0.0	$ 0.0