Debt Lines of Credit (Details) (USD $)	3 Months Ended
	Mar. 31, 2014
Line of Credit Facility [Line Items]
Debt Instrument, Maturity Date	May 01, 2061
500.0 million ability to increase	$ 500,000,000
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	2,170,000,000
Amount restricted/dedicated to support letters of credit	34,674,455
Line of Credit Facility Amount Outstanding Period End	298,000,000
Weighted Average Interest Rate Revolving Credit Facility	0.98%
A 175 billion LOC [Member]
Line of Credit Facility [Line Items]
Unsecured revolving credit facility	$ 1,750,000,000
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line Of Credit Spread	1.05%
Line of Credit [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Line Of Credit Facility Commitment Fee	15 Basis Points
Debt Instrument, Description of Variable Rate Basis	LIBOR plus 1.05%