Restructuring and Related Charges, Pre-tax Restructuring (Credits) Charges (Details) - USD ($) $ in Thousands	3 Months Ended
	Jul. 31, 2018	Jul. 31, 2017
Summary of pre-tax restructuring (credits) charges [Abstract]
Restructuring and related (credits) charges	$ (6,086)	$ 25,729
Restructuring and Reinvestment Program [Member]
Summary of pre-tax restructuring (credits) charges [Abstract]
Restructuring and related (credits) charges	(6,086)	25,729
Restructuring and related charges incurred to date	160,424
Restructuring and Reinvestment Program [Member] | Severance [Member]
Summary of pre-tax restructuring (credits) charges [Abstract]
Restructuring and related (credits) charges	(5,778)	24,721
Restructuring and related charges incurred to date	109,025
Restructuring and Reinvestment Program [Member] | Process Reengineering Consulting [Member]
Summary of pre-tax restructuring (credits) charges [Abstract]
Restructuring and related (credits) charges	135	1,521
Restructuring and related charges incurred to date	20,764
Restructuring and Reinvestment Program [Member] | Other Activities [Member]
Summary of pre-tax restructuring (credits) charges [Abstract]
Restructuring and related (credits) charges	(443)	(513)
Restructuring and related charges incurred to date	30,635
Research [Member] | Restructuring and Reinvestment Program [Member]
Summary of pre-tax restructuring (credits) charges [Abstract]
Restructuring and related (credits) charges	(980)	4,836
Restructuring and related charges incurred to date	24,433
Publishing [Member] | Restructuring and Reinvestment Program [Member]
Summary of pre-tax restructuring (credits) charges [Abstract]
Restructuring and related (credits) charges	(668)	7,254
Restructuring and related charges incurred to date	38,263
Solutions [Member] | Restructuring and Reinvestment Program [Member]
Summary of pre-tax restructuring (credits) charges [Abstract]
Restructuring and related (credits) charges	(257)	2,795
Restructuring and related charges incurred to date	5,990
Corporate Expenses [Member] | Restructuring and Reinvestment Program [Member]
Summary of pre-tax restructuring (credits) charges [Abstract]
Restructuring and related (credits) charges	(4,181)	$ 10,844
Restructuring and related charges incurred to date	$ 91,738