Derivative Financial Instruments Outstanding Interest Rate Swap Agreements (Details) (USD $)	6 Months Ended						6 Months Ended					6 Months Ended		6 Months Ended		6 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2014 Interest Rate Swap 2 [Member]	Jun. 30, 2014 Interest Rate Swap 2 [Member] Notional Period 1 [Member]	Jun. 30, 2014 Interest Rate Swap 2 [Member] Notional Period 2 [Member]	Jun. 30, 2014 Interest Rate Swap 2 [Member] Notional Period 3 [Member]	Jun. 30, 2014 Interest Rate Swap 2 [Member] Notional Period 4 [Member]	Jun. 30, 2014 Interest Rate Swap 3 [Member]	Jun. 30, 2014 Interest Rate Swap 3 [Member] Notional Period 1 [Member]	Jun. 30, 2014 Interest Rate Swap 3 [Member] Notional Period 2 [Member]	Jun. 30, 2014 Interest Rate Swap 3 [Member] Notional Period 3 [Member]	Jun. 30, 2014 Interest Rate Swap 3 [Member] Notional Period 4 [Member]	Jun. 30, 2014 Interest Rate Swap 4 [Member]	Jun. 30, 2014 Interest Rate Swap 4 [Member] Notional Period 1 [Member]	Jun. 30, 2014 Interest Rate Swap 5 [Member]	Jun. 30, 2014 Interest Rate Swap 5 [Member] Notional Period 1 [Member]	Jun. 30, 2014 Interest Rate Swap 6 [Member]	Jun. 30, 2014 Interest Rate Swap 6 [Member] Notional Period 1 [Member]	Jun. 30, 2014 Interest Rate Swap 7 [Member]	Jun. 30, 2014 Interest Rate Swap 7 [Member] Notional Period 1 [Member]	Sep. 30, 2016 Scenario, Forecast [Member]
Derivatives [Line Items]
Effective date		Sep. 30, 2013					Sep. 30, 2014					Sep. 30, 2015		Sep. 30, 2016		Sep. 30, 2016		Sep. 30, 2016
Expiration date		Sep. 30, 2014					Sep. 30, 2015					Sep. 30, 2016		Sep. 30, 2026		Sep. 30, 2026		Sep. 30, 2026
Notional amount			$ 1,350,000,000	$ 1,300,000,000	$ 1,250,000,000	$ 1,200,000,000		$ 1,150,000,000	$ 1,100,000,000	$ 1,050,000,000	$ 1,000,000,000		$ 350,000,000		$ 100,000,000		$ 100,000,000		$ 100,000,000
Pay fixed rate			0.35%	0.35%	0.35%	0.35%
Pay fixed rate, forward interest rate								0.54%	0.54%	0.54%	0.54%		0.93%		2.79%		2.79%		2.80%
Probable Company issued fixed rate debt																				300,000,000
Probable future borrowings																				$ 300,000,000
Derivative settlement date	Sep. 30, 2016