Litigation And Other Related Contingencies (Details)	6 Months Ended
	Oct. 31, 2018 USD ($) securities lawsuit	Apr. 30, 2018 USD ($)	Oct. 31, 2017 USD ($)	Sep. 30, 2016 loan	Sep. 28, 2012 loan
Commitments and Contingencies Disclosure [Abstract]
Loss contingency accrual	$ 3,000,000	$ 2,700,000	$ 2,500,000
Number of loans sold to the trust | loan					96
Loans sold to trust, with claims of breach of contract and indemnity | loan				649
Loss Contingencies [Line Items]
Securitization transactions | securities	39
SCC
Commitments and Contingencies Disclosure [Abstract]
Loss contingency accrual	$ 0	$ 0	$ 4,500,000
Loss Contingencies [Line Items]
Original principal amount of loans securitized	14,000,000,000
Principal assets of SCC	296,000,000
SCC | Claims with Knowledge of Outstanding Principal Amount
Loss Contingencies [Line Items]
Initial principal on loans securitized	$ 3,200,000,000
MGRID LLC v. Merrill Lynch Mortgage Lending Inc
Loss Contingencies [Line Items]
Number of lawsuits | lawsuit	21