Fair Value Measurements (Narratives) (Details) (USD $) In Millions, unless otherwise specified			3 Months Ended		9 Months Ended
	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2012 Nonrecurring [Member]	Dec. 31, 2011 Nonrecurring [Member]	Dec. 31, 2012 Nonrecurring [Member]	Dec. 31, 2011 Nonrecurring [Member]	Dec. 31, 2012 Nonrecurring [Member] Level 3 [Member]	Mar. 31, 2012 Nonrecurring [Member] Level 3 [Member]
Fair Value Measurements [Abstract]
Derivative asset counterparty credit valuation adjustment	$ 1	$ 3
Derivative liability non-performance credit valuation adjustment	1	1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net finance receivables							216	166
Gain (loss) from changes in fair value of net finance receivables			$ 2	$ 4	$ 2	$ 19