Fair Value of Financial Instruments (Schedule of Interest Rate Swaps) (Details) (Interest Rate Swap [Member], USD $)	3 Months Ended
	Mar. 31, 2014
Derivative [Line Items]
Notional Amount, Liability	$ 2,000,000,000
Interest Rate Swaps One [Member]
Derivative [Line Items]
Notional Amount, Liability	100,000,000
Fixed Interest Rate	5.231%
Termination Date	Jul. 25, 2014
Fair Value of Liability	2,000,000
Interest Rate Swaps Two [Member]
Derivative [Line Items]
Notional Amount, Liability	100,000,000
Fixed Interest Rate	5.231%
Termination Date	Jul. 25, 2014
Fair Value of Liability	2,000,000
Interest Rate Swaps Three [Member]
Derivative [Line Items]
Notional Amount, Liability	200,000,000
Fixed Interest Rate	5.16%
Termination Date	Jul. 25, 2014
Fair Value of Liability	3,000,000
Interest Rate Swaps Four [Member]
Derivative [Line Items]
Notional Amount, Liability	75,000,000
Fixed Interest Rate	5.041%
Termination Date	Jul. 25, 2014
Fair Value of Liability	1,000,000
Interest Rate Swaps Five [Member]
Derivative [Line Items]
Notional Amount, Liability	125,000,000
Fixed Interest Rate	5.022%
Termination Date	Jul. 25, 2014
Fair Value of Liability	2,000,000
Interest Rate Swaps Six [Member]
Derivative [Line Items]
Notional Amount, Liability	100,000,000
Fixed Interest Rate	2.621%
Termination Date	Jul. 25, 2014
Fair Value of Liability	1,000,000
Interest Rate Swaps Seven [Member]
Derivative [Line Items]
Notional Amount, Liability	100,000,000
Fixed Interest Rate	3.11%
Termination Date	Jul. 25, 2014
Fair Value of Liability	1,000,000
Interest Rate Swaps Eight [Member]
Derivative [Line Items]
Notional Amount, Liability	100,000,000
Fixed Interest Rate	3.258%
Termination Date	Jul. 25, 2014
Fair Value of Liability	1,000,000
Interest Rate Swaps Nine [Member]
Derivative [Line Items]
Notional Amount, Liability	200,000,000
Fixed Interest Rate	2.693%
Termination Date	Oct. 26, 2014
Fair Value of Liability	3,000,000
Interest Rate Swaps Ten [Member]
Derivative [Line Items]
Notional Amount, Liability	300,000,000
Fixed Interest Rate	3.447%
Termination Date	Aug. 08, 2016
Fair Value of Liability	19,000,000
Interest Rate Swaps Eleven [Member]
Derivative [Line Items]
Notional Amount, Liability	200,000,000
Fixed Interest Rate	3.429%
Termination Date	Aug. 19, 2016
Fair Value of Liability	13,000,000
Interest Rate Swaps Twelve [Member]
Derivative [Line Items]
Notional Amount, Liability	100,000,000
Fixed Interest Rate	3.401%
Termination Date	Aug. 19, 2016
Fair Value of Liability	6,000,000
Interest Rate Swaps Thirteen [Member]
Derivative [Line Items]
Notional Amount, Liability	200,000,000
Fixed Interest Rate	3.50%
Termination Date	Aug. 30, 2016
Fair Value of Liability	13,000,000
Interest Rate Swaps Fourteen [Member]
Derivative [Line Items]
Notional Amount, Liability	100,000,000
Fixed Interest Rate	3.005%
Termination Date	Nov. 30, 2016
Fair Value of Liability	6,000,000
Interest Rate Swaps Fifteen [Member]
Derivative [Line Items]
Notional Amount, Liability	200,000,000
Fixed Interest Rate	2.055%
Termination Date	Jul. 25, 2019
Fair Value of Asset		[1]
Interest Rate Swaps Sixteen [Member]
Derivative [Line Items]
Notional Amount, Liability	200,000,000
Fixed Interest Rate	2.059%
Termination Date	Jul. 25, 2019
Fair Value of Asset		[1]
Interest Rate Swaps Seventeen [Member]
Derivative [Line Items]
Notional Amount, Liability	200,000,000
Fixed Interest Rate	2.613%
Termination Date	Aug. 30, 2019
Fair Value of Liability		[2]
Interest Rate Swaps Eighteen [Member]
Derivative [Line Items]
Notional Amount, Liability	300,000,000
Fixed Interest Rate	2.892%
Termination Date	Aug. 30, 2020
Fair Value of Liability		[2]

[1] This interest rate swap becomes effective July 25, 2014.

[2] This interest rate swap becomes effective August 30, 2015.