Risk Management Activities and Fair Value Measurements - Derivative Notional Amounts and Fair Value (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Jun. 30, 2012
Cash Flow Hedging [Member]
Derivative [Line Items]
Notional amount	$ 951	$ 831
Fair Value Asset (Liability)	63	(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	951	831
Fair Value Asset (Liability)	63	(142)
Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Notional amount	9,150	10,747
Fair Value Asset (Liability)	323	298
Net Investment Hedging [Member]
Derivative [Line Items]
Notional amount	1,705	1,768
Fair Value Asset (Liability)	139	13
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional amount	11,969	13,335
Fair Value Asset (Liability)	(20)	64
Not Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Notional amount	11,946	13,210
Fair Value Asset (Liability)	(19)	63
Not Designated as Hedging Instrument [Member] | Commodity Contract [Member]
Derivative [Line Items]
Notional amount	23	125
Fair Value Asset (Liability)	$ (1)	$ 1