Interest Rate Swaps in Effect (Details) (USD $)	6 Months Ended
	Jun. 30, 2012
Interest Rate Swap 1
Debt Disclosure [Line Items]
Notional Amount	$ 20,000,000,000
Fixed Interest Rate	1.80%
Effective Date	Nov. 23, 2009
Maturity Date	Nov. 23, 2012
Interest Rate Swap 2
Debt Disclosure [Line Items]
Notional Amount	20,000,000,000
Fixed Interest Rate	1.56%
Effective Date	Mar. 11, 2010
Maturity Date	Dec. 11, 2012
Interest Rate Swap 3
Debt Disclosure [Line Items]
Notional Amount	15,000,000,000
Fixed Interest Rate	0.95%
Effective Date	Aug. 06, 2010
Maturity Date	Dec. 06, 2012
Interest Rate Swap 4
Debt Disclosure [Line Items]
Notional Amount	25,000,000,000
Fixed Interest Rate	1.61%
Effective Date	Feb. 23, 2011
Maturity Date	Feb. 24, 2014
Interest Rate Swap 5
Debt Disclosure [Line Items]
Notional Amount	25,000,000,000
Fixed Interest Rate	2.52%
Effective Date	Feb. 23, 2011
Maturity Date	Feb. 23, 2016
Interest Rate Swap 6
Debt Disclosure [Line Items]
Notional Amount	25,000,000,000
Fixed Interest Rate	0.975%
Effective Date	Jul. 18, 2011
Maturity Date	Jul. 18, 2014
Interest Rate Swap 7
Debt Disclosure [Line Items]
Notional Amount	15,000,000,000
Fixed Interest Rate	1.185%
Effective Date	Sep. 12, 2011
Maturity Date	Sep. 12, 2016
Interest Rate Swap 8
Debt Disclosure [Line Items]
Notional Amount	$ 15,000,000,000
Fixed Interest Rate	0.62%
Effective Date	Sep. 12, 2011
Maturity Date	Sep. 11, 2014