Fair Value (Fair Value Measurement - Nonrecurring Basis) (Details) (Fair Value, Measurements, Nonrecurring [Member], USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Mar. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Held-for-sale, Other	$ 18
Mortgages Held-for-sale, Fair Value Disclosure		580
Commercial Finance Receivables and Loans, Net, Fair Value	167	158
Assets, Fair Value Disclosure	191	821
Lower of cost or fair value or valuation reserve allowance	0
Mortgage Loans Held-For-Sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Lower of cost or fair value or valuation reserve allowance		(57)
Commercial Finance Receivables And Loans, Automotive [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial Finance Receivables and Loans, Net, Fair Value	121	122
Lower of cost or fair value or valuation reserve allowance	(21)	(25)
Commercial Finance Receivables And Loans, Mortgage [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial Finance Receivables and Loans, Net, Fair Value		16
Lower of cost or fair value or valuation reserve allowance		(11)
Commercial Finance Receivables And Loans, Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial Finance Receivables and Loans, Net, Fair Value	46	20
Lower of cost or fair value or valuation reserve allowance	(7)	(10)
Commercial Loan [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Lower of cost or fair value or valuation reserve allowance	(28)	(46)
Repossessed And Foreclosed Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Assets, Fair Value Disclosure	6	83
Lower of cost or fair value or valuation reserve allowance	(4)	(13)
Assets, Total [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Lower of cost or fair value or valuation reserve allowance	(32)	(116)
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Held-for-sale, Other	0
Mortgages Held-for-sale, Fair Value Disclosure		0
Commercial Finance Receivables and Loans, Net, Fair Value	0	0
Assets, Fair Value Disclosure	0	0
Fair Value, Inputs, Level 1 [Member] | Commercial Finance Receivables And Loans, Automotive [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial Finance Receivables and Loans, Net, Fair Value	0	0
Fair Value, Inputs, Level 1 [Member] | Commercial Finance Receivables And Loans, Mortgage [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial Finance Receivables and Loans, Net, Fair Value		0
Fair Value, Inputs, Level 1 [Member] | Commercial Finance Receivables And Loans, Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial Finance Receivables and Loans, Net, Fair Value	0	0
Fair Value, Inputs, Level 1 [Member] | Repossessed And Foreclosed Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Assets, Fair Value Disclosure	0	0
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Held-for-sale, Other	0
Mortgages Held-for-sale, Fair Value Disclosure		0
Commercial Finance Receivables and Loans, Net, Fair Value	0	1
Assets, Fair Value Disclosure	0	63
Fair Value, Inputs, Level 2 [Member] | Commercial Finance Receivables And Loans, Automotive [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial Finance Receivables and Loans, Net, Fair Value	0	0
Fair Value, Inputs, Level 2 [Member] | Commercial Finance Receivables And Loans, Mortgage [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial Finance Receivables and Loans, Net, Fair Value		1
Fair Value, Inputs, Level 2 [Member] | Commercial Finance Receivables And Loans, Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial Finance Receivables and Loans, Net, Fair Value	0	0
Fair Value, Inputs, Level 2 [Member] | Repossessed And Foreclosed Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Assets, Fair Value Disclosure	0	62
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Held-for-sale, Other	18
Mortgages Held-for-sale, Fair Value Disclosure		580
Commercial Finance Receivables and Loans, Net, Fair Value	167	157
Assets, Fair Value Disclosure	191	758
Fair Value, Inputs, Level 3 [Member] | Commercial Finance Receivables And Loans, Automotive [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial Finance Receivables and Loans, Net, Fair Value	121	122
Fair Value, Inputs, Level 3 [Member] | Commercial Finance Receivables And Loans, Mortgage [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial Finance Receivables and Loans, Net, Fair Value		15
Fair Value, Inputs, Level 3 [Member] | Commercial Finance Receivables And Loans, Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commercial Finance Receivables and Loans, Net, Fair Value	46	20
Fair Value, Inputs, Level 3 [Member] | Repossessed And Foreclosed Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Assets, Fair Value Disclosure	$ 6	$ 21