Segment Information (Details) - USD ($) $ in Thousands		3 Months Ended							9 Months Ended				12 Months Ended
		Oct. 31, 2018		Jan. 31, 2018	Oct. 31, 2017		Jul. 31, 2017	Apr. 30, 2017	Oct. 31, 2018		Oct. 31, 2017		Jan. 31, 2018
Segment Reporting Information
Revenues		$ 9,340,029		$ 10,033,397	$ 8,448,471		$ 8,092,353	$ 7,023,620	$ 26,774,449		$ 23,564,444		$ 33,597,841
Operating income:		146,888			79,567				327,749		258,176
Stock-based compensation expense		(8,139)			(8,325)				(23,694)		(21,217)
Depreciation and amortization:		39,242			42,334				119,641		112,907
Capital expenditures:		17,430			172,166				40,153		213,979
Identifiable assets:		12,559,603		12,920,359					12,559,603				12,920,359
Long-lived assets:		268,304		279,091					268,304				279,091
Goodwill & acquisition-related intangible assets, net:		1,778,390		1,914,500					1,778,390				1,914,500
Legal settlements and other, net		(7,207)			0				(15,406)		(41,343)
Acquisition, integration and restructuring expenses		20,277			29,748				66,799		101,931
Other Tax Expense (Benefit)		(5,500)							(6,100)
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal		29			0				6,746		0
Americas
Segment Reporting Information
Revenues	[1]	4,137,852			3,663,498				11,799,389		10,568,516
Operating income:		112,399	[2]		55,551	[2]			261,671	[3]	194,426	[3]
Depreciation and amortization:		$ 23,394			$ 24,645				$ 70,244		$ 62,308
Sales to unaffiliated customers, as percentage of total sales		91.00%			89.00%				90.00%		89.00%
Capital expenditures:		$ 11,493			$ 167,210				$ 24,105		$ 195,169
Identifiable assets:		5,539,656		5,014,409					5,539,656				5,014,409
Long-lived assets:	[1]	212,124		214,922					212,124				214,922
Goodwill & acquisition-related intangible assets, net:		$ 1,097,610		$ 1,139,273					$ 1,097,610				$ 1,139,273
Long-lived assets, as percentage of total assets		97.00%		97.00%					97.00%				97.00%
Legal settlements and other, net		$ (7,200)							$ (15,400)		(42,600)
Allowance for Doubtful Accounts Receivable, Recoveries		25,000							25,000
Acquisition, integration and restructuring expenses		6,000			14,100				19,000		58,600
Europe
Segment Reporting Information
Revenues		4,920,156			4,518,669				14,130,985		12,269,044
Operating income:	[5]	39,889	[4]		29,909				86,292	[4],[6]	73,172
Depreciation and amortization:		13,679			15,734				42,686		44,957
Capital expenditures:		4,742			4,450				13,821		16,764
Identifiable assets:		6,435,338		$ 7,336,974					6,435,338				$ 7,336,974
Long-lived assets:		50,968		57,781					50,968				57,781
Goodwill & acquisition-related intangible assets, net:		576,465		645,134					576,465				645,134
Acquisition, integration and restructuring expenses		13,100			14,100				44,400		40,400
Other Tax Expense (Benefit)		(5,500)							(6,500)
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal									6,700
Asia-Pacific
Segment Reporting Information
Revenues		282,021			266,304				844,075		726,884
Operating income:		2,739			2,432				3,480		11,795
Depreciation and amortization:		2,169			1,955				6,711		5,642
Capital expenditures:		1,195			$ 506				2,227		$ 2,046
Identifiable assets:		584,609		568,976					584,609				568,976
Long-lived assets:		5,212		6,388					5,212				6,388
Goodwill & acquisition-related intangible assets, net:		$ 104,315		$ 130,093					$ 104,315				$ 130,093

[1] Net sales in the United States represented 91% and 89%, respectively, of the total Americas' net sales for the three months ended October 31, 2018 and 2017, and 90% and 89% of the total Americas' net sales for the nine months ended October 31, 2018 and 2017. Total long-lived assets in the United States represented 97% of the Americas' total long-lived assets at both October 31, 2018 and January 31, 2018.

[2] Operating income in the Americas for the three months ended October 31, 2018 and 2017 includes acquisition, integration and restructuring expenses of $6.0 million and $14.1 million, respectively (see further discussion in Note 5 – Acquisition, Integration and Restructuring Expenses). Operating income in the Americas includes a gain related to legal settlements and other, net, of $7.2 million for the three months ended October 31, 2018 (see further discussion in Note 1 - Business and Summary of Significant Accounting Policies). Operating income in the Americas for the three months ended October 31, 2018 includes a benefit of approximately $25 million related to the collection of an accounts receivable balance previously considered uncollectible.

[3] Operating income in the Americas for the nine months ended October 31, 2018 and 2017 includes acquisition, integration and restructuring expenses of $19.0 million and $58.6 million, respectively, and a gain related to legal settlements and other, net, of $15.4 million and $42.6 million, respectively. Operating income in the Americas for the nine months ended October 31, 2018 includes a benefit of approximately $25 million related to the collection of an accounts receivable balance previously considered uncollectible.

[4] Operating income in Europe for the three and nine months ended October 31, 2018 includes expenses of $5.5 million and $6.5 million, respectively, related to the recognition of certain tax indemnification liabilities (see further discussion in Note 8 – Income Taxes).

[5] Operating income in Europe for the three months ended October 31, 2018 and 2017 includes acquisition, integration and restructuring expenses of $13.1 million and $14.1 million, respectively. Operating income in Europe for the nine months ended October 31, 2018 and 2017, includes acquisition, integration and restructuring expenses of $44.4 million and $40.4 million, respectively.

[6] Operating income in Europe for the nine months ended October 31, 2018 includes a gain on disposal of a subsidiary of $6.7 million (see further discussion in Note 6 – Gain on Disposal of Subsidiary).