Postretirement Benefits (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Jun. 30, 2014
Pension Benefits
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service Cost	$ 73	$ 74
Interest Cost	143	140
Expected Return on Plan Assets	(170)	(148)
Amortization of Deferred Amounts	6	3
Recognized Net Actuarial Loss	52	53
Gross Benefit Cost (Credit)	104	122
Dividends on ESOP Preferred Stock	0	0
Net Periodic Benefit Cost (Credit)	104	122
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Expected Long-term Return on Assets			7.20%
Other Retiree Benefits
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service Cost	37	47
Interest Cost	64	64
Expected Return on Plan Assets	(96)	(95)
Amortization of Deferred Amounts	(5)	(5)
Recognized Net Actuarial Loss	29	50
Gross Benefit Cost (Credit)	29	61
Dividends on ESOP Preferred Stock	(16)	(17)
Net Periodic Benefit Cost (Credit)	$ 13	$ 44
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Expected Long-term Return on Assets			8.30%