Revenues - Impact of Adoption (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended			6 Months Ended
		Nov. 30, 2018		Nov. 30, 2017	Nov. 30, 2018		Nov. 30, 2017	May 31, 2018
Statement of Financial Position [Abstract]
Accounts receivable, net		$ 377.3		$ 262.4	$ 377.3		$ 262.4	$ 204.9
Inventories, net		365.6		355.7	365.6		355.7	294.9
Prepaid expenses and other current assets		71.3		69.2	71.3		69.2	66.6
Noncurrent deferred income taxes		41.4		47.6	41.4		47.6	25.2
Deferred revenue		187.2		82.0	187.2		82.0	24.7
Other accrued expenses		227.8		173.7	227.8		173.7	177.9
Retained earnings		1,018.4		1,074.1	1,018.4		1,074.1	1,065.2
Book fair incentive credits		9.2		37.4	9.2		37.4	35.8
Returns liability		78.7		0.0	78.7		0.0	0.0
Income Statement [Abstract]
Revenues		604.7		598.3	823.1		787.5
Cost of goods sold		262.4		253.6	387.7		369.2
Selling, general and administrative expenses		229.7		227.7	393.4		387.2
Provision for losses on accounts receivable		2.7		4.3	4.1		6.2
Depreciation and amortization		14.4		9.8	27.6		19.0
Operating income (loss)		98.2		107.2	14.4		5.4
Interest income (expense), net		0.5		0.0	1.3		0.3
Other components of net periodic benefit (cost)		(0.3)		(15.5)	(0.7)		(15.6)
Provision (benefit) for income taxes		26.8		34.6	4.7		(3.3)
Net income (loss)		$ 71.6		$ 57.1	$ 10.3		$ (6.6)
Basic earnings (loss) (in Dollars per share)		$ 2.03		$ 1.63	$ 0.29		$ (0.19)
Diluted earnings (loss) (in Dollars per share)		$ 1.99		$ 1.60	$ 0.29		$ (0.19)
ASU 2014-09 | Adjustments due to adoption
Statement of Financial Position [Abstract]
Accounts receivable, net	[1]							31.1
Inventories, net	[2]							(1.9)
Prepaid expenses and other current assets	[2],[3]							(4.3)
Noncurrent deferred income taxes	[4]							16.0
Deferred revenue	[5]							86.3
Other accrued expenses	[6]							1.1
Retained earnings								(46.5)
Book fair incentive credits								27.2
Returns liability								28.3
Income Statement [Abstract]
Revenues		$ 10.8	[7]		$ (1.7)	[8]
Cost of goods sold		2.6	[7]		(1.5)	[8]
Selling, general and administrative expenses	[9]	2.6			(0.6)
Depreciation and amortization		0.0			0.0
Operating income (loss)		5.6			0.4
Interest income (expense), net		0.0			0.0
Other components of net periodic benefit (cost)		0.0			0.0
Provision (benefit) for income taxes		1.5			0.1	[10]
Net income (loss)		$ 4.1			$ 0.3
Basic earnings (loss) (in Dollars per share)		$ 0.12			$ 0.01
Diluted earnings (loss) (in Dollars per share)		$ 0.11			$ 0.01
ASU 2014-09 | Adjusted balance
Statement of Financial Position [Abstract]
Accounts receivable, net								236.0
Inventories, net								293.0
Prepaid expenses and other current assets								62.3
Noncurrent deferred income taxes								41.2
Deferred revenue								111.0
Other accrued expenses								179.0
Retained earnings								$ 1,018.7
Income Statement [Abstract]
Revenues		$ 615.5			$ 821.4
Cost of goods sold		265.0			386.2
Selling, general and administrative expenses		232.3			392.8
Depreciation and amortization		14.4			27.6
Operating income (loss)		103.8			14.8
Interest income (expense), net		0.5			1.3
Other components of net periodic benefit (cost)		(0.3)			(0.7)
Provision (benefit) for income taxes		28.3			4.8
Net income (loss)		$ 75.7			$ 10.6
Basic earnings (loss) (in Dollars per share)		$ 2.15			$ 0.30
Diluted earnings (loss) (in Dollars per share)		$ 2.10			$ 0.30

[1] Primarily represents the reclassification of the Company’s accounting for estimated returns from a reduction to Accounts receivable, net, to a current liability within Other accrued expenses.

[2] Represents the reclassification of a return asset from Inventory to Prepaid expenses and other current assets.

[3] Primarily represents the adjustment for previously capitalized direct response advertising costs.

[4] Represents the income tax impact of Topic 606 adjustments.

[5] Represents the deferred revenue related to outstanding book fairs incentive credits as of June 1, 2018.

[6] Represents a reduction to Other accrued expenses of $27.2 for outstanding book fair incentive credits as of June 1, 2018. This decrease was offset by a $28.3 increase for estimated returns recorded to Other accrued expenses.

[7] Represents additional deferred revenue and cost of goods sold on incentive credits awarded during the period, partially offset by incremental revenue and cost of goods sold related to the redemption of book fairs incentive credits.

[8] Represents incremental revenue and cost of goods sold related to the redemption of book fairs incentive program credits, partially offset by additional deferred revenue on incentive credits awarded during the period.

[9] Represents direct response advertising costs being expensed as incurred.

[10] Represents the income tax impact of Topic 606 adjustments.