Related Party Transactions (Narratives) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Mar. 31, 2012
Related Party Transaction [Line Items]
Credit Support Fees	$ 8	$ 8
Notes Payable	47		61
Loans payable to affiliate	0		2,201
Notes Receivable	612		1,052
Accounts Receivable	17		17
Accounts Payable	32		58
Subvention Revenues	226	243
Stock-based Compensation Expense	2		2
Operating Leases to Affiliates	4		4
Employee benefits expense	7	10
Commercial paper issued by affiliated entity	$ 0		$ 0