Risk Management Activities and Fair Value Measurements - Derivative Notional Amounts and Fair Value (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Jun. 30, 2012
Cash Flow Hedging [Member]
Derivative [Line Items]
Notional amount	$ 831	$ 831
Fair Value Asset (Liability)	(162)	(142)
Cash Flow Hedging [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Notional amount	0	0
Fair Value Asset (Liability)	0	0
Cash Flow Hedging [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Notional amount	831	831
Fair Value Asset (Liability)	(162)	(142)
Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Notional amount	10,894	10,747
Fair Value Asset (Liability)	338	298
Net Investment Hedging [Member]
Derivative [Line Items]
Notional amount	1,741	1,768
Fair Value Asset (Liability)	(27)	13
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional amount	13,627	13,335
Fair Value Asset (Liability)	88	64
Not Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Notional amount	13,477	13,210
Fair Value Asset (Liability)	89	63
Not Designated as Hedging Instrument [Member] | Commodity Contract [Member]
Derivative [Line Items]
Notional amount	150	125
Fair Value Asset (Liability)	$ (1)	$ 1