Debt and Equity Transactions (Unaudited) Credit Facility (Details) (USD $)	6 Months Ended
	Jun. 30, 2011
Line of Credit Facility [Line Items]
Debt Instrument, Maturity Date	March 30, 2016
Line of Credit Facility, Maximum Borrowing Capacity	$ 1,500,000,000
Amount of revolving credit facility available to subsidiary	500,000,000
Letters of Credit Outstanding, Amount	43,000,000
Line of Credit Facility, Amount Outstanding	0
Line of Credit Facility, Remaining Borrowing Capacity	$ 1,500,000,000
Line of Credit [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Description of Variable Rate Basis	LIBOR
Debt Instrument, Basis Spread on Variable Rate (in hundredths)	2.00%