Significant Observable And Unobservable Inputs (Detail) (Recurring Basis, Level 3)	12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
30 to 59 day delinquency rate	2.00%	1.20%
60 to 89 day delinquency rate	0.70%	0.60%
90 plus day delinquency rate	2.40%	1.10%
Loss severity	39.90%	39.50%
Coupon rate	5.00%	5.00%
Month 1 to month 24 constant default rate	4.50%	3.40%
Discount rate	4.00%	4.00%
Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
30 to 59 day delinquency rate	4.60%	4.80%
60 to 89 day delinquency rate	3.10%	2.50%
90 plus day delinquency rate	6.20%	6.00%
Loss severity	71.20%	71.70%
Coupon rate	6.00%	7.50%
Current credit support	58.40%	25.30%
Month 1 to month 24 constant default rate	11.50%	11.30%
Discount rate	7.00%	12.00%