Risk Management Activities and Fair Value Measurements - Derivative Notional Amounts and Fair Value (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Jun. 30, 2013
Cash Flow Hedging [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Notional amount	$ 951	$ 951
Fair Value Asset (Liability)	164	168
Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Notional amount	10,226	9,117
Fair Value Asset (Liability)	103	132
Net Investment Hedging [Member]
Derivative [Line Items]
Notional amount	1,303	1,303
Fair Value Asset (Liability)	223	233
Not Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Notional amount	6,496	7,080
Fair Value Asset (Liability)	$ (2)	$ (71)