Debt Lines of Credit (Details) (USD $)	6 Months Ended
	Jun. 30, 2013
Line of Credit Facility [Line Items]
Debt Instrument, Maturity Date	Sep. 01, 2014
500.0 million ability to increase	$ 500,000,000
Line Of Credit Facility Commitment Fee	15 Basis Points
A 250 billion LOC [Member] [Domain]
Line of Credit Facility [Line Items]
Unsecured revolving credit facility	2,500,000,000
Debt Instrument, Maturity Date	Apr. 01, 2018
Remaining borrowing capacity	2,470,000,000
Amount restricted/dedicated to support letters of credit	33,251,523
Weighted Average Interest Rate Revolving Credit Facility	1.27%
A 175 billion LOC [Member]
Line of Credit Facility [Line Items]
Unsecured revolving credit facility	$ 1,750,000,000
Debt Instrument, Maturity Date	Jul. 01, 2014
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line Of Credit Spread	1.05%