Risk Management Activities and Fair Value Measurements Risk Management Activities and Fair Value Measurements - Additional Information (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Jun. 30, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long Term Debt, Current Maturities measured at Fair Value	$ 2,513	$ 4,095
Long-term Debt, Fair Value	455
Fair Value, Measurements, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative, Net Liability Position, Aggregate Fair Value	47
US Treasury and Government [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Amortized Cost Basis	$ 1,504	$ 0