Postretirement Benefits (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Jun. 30, 2013	Jun. 30, 2012
Pension Benefits
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service Cost	$ 74	$ 67
Interest Cost	140	157
Expected Return on Plan Assets	(148)	(146)
Amortization of Deferred Amounts	3	6
Recognized Net Actuarial Loss	53	26
Gross Benefit Cost (Credit)	122	110
Dividends on ESOP Preferred Stock	0	0
Net Periodic Benefit Cost (Credit)	122	110
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Expected Long-term Return on Assets			7.30%	7.40%
Other Retiree Benefits
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service Cost	47	36
Interest Cost	64	69
Expected Return on Plan Assets	(95)	(108)
Amortization of Deferred Amounts	(5)	(5)
Recognized Net Actuarial Loss	50	25
Gross Benefit Cost (Credit)	61	17
Dividends on ESOP Preferred Stock	(17)	(19)
Net Periodic Benefit Cost (Credit)	$ 44	$ (2)
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Expected Long-term Return on Assets			8.30%	9.20%