Short-Term Financing (Details) (USD $)	9 Months Ended	12 Months Ended			12 Months Ended
	Mar. 31, 2012	Jun. 30, 2012 Short-Term Commercial Paper Program [Member]	Jun. 30, 2011 Short-Term Commercial Paper Program [Member]	Mar. 31, 2012 Short-Term Commercial Paper Program [Member]	Jun. 30, 2012 364-Day Credit Agreement [Member]	Jun. 30, 2012 Credit Facility Maturing In June 2015 [Member]	Jun. 30, 2012 Credit Facility Maturing In June 2017 [Member]	Jun. 30, 2012 Reverse Repurchase Agreements [Member]	Jun. 30, 2011 Reverse Repurchase Agreements [Member]	Jun. 30, 2012 Issuance Of Debt [Member]
Short-term Debt [Line Items]
Maximum borrowing capacity under credit facilities					$ 2,000,000,000	$ 3,250,000,000	$ 1,500,000,000	$ 3,000,000,000
Credit agreement period					364 days			5 days
Expiration date of credit facilities					Jun. 01, 2013	Jun. 01, 2015	Jun. 01, 2017
Line of credit facility potentially available increase in maximum borrowing capacity						500,000,000	500,000,000
Aggregate amount of commercial paper issuable under the short-term commercial paper program										6,750,000,000
Average outstanding borrowings		2,300,000,000	1,600,000,000					297,700,000	505,200,000
Weighted average interest rates		0.10%	0.20%					0.60%	0.40%
Outstanding borrowings			$ 0	$ 0					$ 0
Weighted average maturity of borrowings under the short-term commercial paper program		2 days	2 days
Maturities of commercial paper range	overnight to up to 364 days
Maturities of short-term funding agreements	overnight to up to five business days
Term of credit						4 years	5 years