Postretirement Benefits (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013	Mar. 31, 2012	Jun. 30, 2013	Jun. 30, 2012
Pension Benefits
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service Cost	$ 76	$ 62	$ 226	$ 192
Interest Cost	140	149	421	458
Expected Return on Plan Assets	(146)	(140)	(442)	(428)
Amortization of Deferred Amounts	4	6	13	17
Recognized Net Actuarial Loss	55	25	161	77
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Curtailments			2	0
Defined Benefit Plan Curtailments And Settlements	2	0	2	0
Gross Benefit Cost (Credit)	131	102	383	316
Dividends on ESOP Preferred Stock	0	0	0	0
Net Periodic Benefit Cost (Credit)	131	102	383	316
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	48	35	143	106
Interest Cost	65	69	195	207
Expected Return on Plan Assets	(95)	(109)	(286)	(325)
Amortization of Deferred Amounts	(5)	(5)	(15)	(15)
Recognized Net Actuarial Loss	49	25	149	74
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Curtailments			0	0
Defined Benefit Plan Curtailments And Settlements	0	0	0	0
Gross Benefit Cost (Credit)	62	15	186	47
Dividends on ESOP Preferred Stock	(17)	(19)	(52)	(56)
Net Periodic Benefit Cost (Credit)	$ 45	$ (4)	$ 134	$ (9)
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Expected Long-term Return on Assets					8.30%	9.20%