Restructuring and Related Charges, Pre-tax Restructuring Charges (Details) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2016
Restructuring Cost and Reserve [Line Items]
Restructuring and related charges	$ 28,566	$ 13,355	$ 28,611
Restructuring and Reinvestment Program [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and related charges	28,566	13,355	28,611
Restructuring and related charges incurred to date	166,510
Restructuring and Reinvestment Program [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and related charges	27,213	8,386	16,443
Restructuring and related charges incurred to date	114,803
Restructuring and Reinvestment Program [Member] | Process Reengineering Consulting [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and related charges	1,815	148	7,191
Restructuring and related charges incurred to date	20,629
Restructuring and Reinvestment Program [Member] | Other Activities [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and related charges	(462)	4,821	4,977
Restructuring and related charges incurred to date	31,078
Research [Member] | Restructuring and Reinvestment Program [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and related charges	5,257	1,949	2,982
Restructuring and related charges incurred to date	25,413
Publishing [Member] | Restructuring and Reinvestment Program [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and related charges	6,443	1,596	4,507
Restructuring and related charges incurred to date	38,931
Solutions [Member] | Restructuring and Reinvestment Program [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and related charges	3,695	1,787	1,042
Restructuring and related charges incurred to date	6,247
Corporate Expenses [Member] | Restructuring and Reinvestment Program [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and related charges	13,171	$ 8,023	$ 20,080
Restructuring and related charges incurred to date	$ 95,919