Related Party Transactions (Narratives) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Mar. 31, 2014
Related Party Transaction [Line Items]
Credit Support Fees	$ 21	$ 20
Notes Payable	23		22
Notes Receivable	790		1,172
Accounts Receivable	76		74
Accounts Payable	236		216
Subvention Revenues	273	232
Stock-based Compensation Expense	2		2
Operating Leases to Affiliates	7		7
Employee benefits expense	6	9
Investments in affiliates' commercial paper	$ 16		$ 0