Stockholders' Equity (Share Repurchases) (Details) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	3 Months Ended
Apr. 30, 2015	Jan. 31, 2015	Apr. 30, 2014	Jan. 31, 2014	Dec. 15, 2011
Equity [Abstract]
Share Repurchase Program, maximum amount authorized					$ 500.0
Number of common stock repurchased, shares	0us-gaap_TreasuryStockSharesAcquired	100us-gaap_TreasuryStockSharesAcquired	0us-gaap_TreasuryStockSharesAcquired	396us-gaap_TreasuryStockSharesAcquired
Cost of common stock repurchased		16.0		50.0
Average purchase price per share		$ 159.96		$ 126.21
Share Repurchase Program, remaining authorized amount	$ 169.7

Final price paid per share for the purchase of the targeted number of shares, determined by an average market price over a fixed period of time.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 30

-Section 25

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6405686&loc=d3e22802-112653

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- Definition

Amount of stock repurchase plan authorized.

+ References

No definition available.

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- Definition

Amount remaining of a stock repurchase plan authorized.

+ References

No definition available.

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- Definition

Number of shares that have been repurchased during the period and are being held in treasury.

+ References

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- Definition

Equity impact of the cost of common and preferred stock that were repurchased during the period. Recorded using the cost method.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.3-04)

-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 30

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6405813&loc=d3e23239-112655

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