Loss Contingencies Arising From Representations And Warranties Of Our Discontinued Mortgage Operations (Claims Received By Loan Origination Year) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended				57 Months Ended
	Jan. 31, 2013	Apr. 30, 2012	Apr. 30, 2011	Apr. 30, 2010	Apr. 30, 2009	Jan. 31, 2013
Commitments And Contingencies [Line Items]
Claims received for loans	$ 168	$ 1,092	$ 218	$ 145	$ 432	$ 2,055
2005 [Member]
Commitments And Contingencies [Line Items]
Claims received for loans	22	4	8	15	62	111
2006 [Member]
Commitments And Contingencies [Line Items]
Claims received for loans	133	325	194	108	217	977
2007 [Member]
Commitments And Contingencies [Line Items]
Claims received for loans	$ 13	$ 763	$ 16	$ 22	$ 153	$ 967