Postretirement Benefits (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2012	Mar. 31, 2011	Jun. 30, 2012
Pension Benefits
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service Cost	$ 62	$ 65	$ 192	$ 191
Interest Cost	149	146	458	430
Expected Return on Plan Assets	(140)	(123)	(428)	(364)
Amortization of Deferred Amounts	6	4	17	13
Recognized Net Actuarial Loss	25	39	77	114
Gross Benefit Cost (Credit)	102	131	316	384
Dividends on ESOP Preferred Stock	0	0	0	0
Net Periodic Benefit Cost (Credit)	102	131	316	384
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Expected Long-term Return on Assets					7.40%
Other Retiree Benefits
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service Cost	35	40	106	110
Interest Cost	69	72	207	203
Expected Return on Plan Assets	(109)	(108)	(325)	(323)
Amortization of Deferred Amounts	(5)	(3)	(15)	(13)
Recognized Net Actuarial Loss	25	25	74	72
Gross Benefit Cost (Credit)	15	26	47	49
Dividends on ESOP Preferred Stock	(19)	(20)	(56)	(59)
Net Periodic Benefit Cost (Credit)	$ (4)	$ 6	$ (9)	$ (10)
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Expected Long-term Return on Assets					9.20%