Risk Management Activities and Fair Value Measurements - Derivative Notional Amounts and Fair Value (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Jun. 30, 2014
Cash Flow Hedging [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Notional amount	$ 951	$ 951
Fair Value Asset (Liability)	300	187
Fair Value Hedging [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Notional amount	8,128	9,738
Fair Value Asset (Liability)	251	168
Net Investment Hedging [Member]
Derivative [Line Items]
Notional amount	855	831
Fair Value Asset (Liability)	164	48
Not Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Notional amount	8,714	12,111
Fair Value Asset (Liability)	$ (143)	$ (42)