Stockholder's Equity (Details 1) (USD $)	3 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2012
Summary of common stock issuances
Dividend reinvestment plan issuances, Shares Issued		2,379,609	1,485,598
Dividend reinvestment plan issuances, Average Price		$ 64.62	$ 55.65
Dividend reinvestment plan issuances, Net Proceeds		153,762,000	82,678,000
Dividend reinvestment plan issuances, Gross Proceeds		153,762,000	82,678,000
Option exercises, Shares		200,467	155,195
Option exercises, Average Price		42.45	39.61
Option exercises, Gross Proceeds		8,509,000	6,147,000
Option exercises, Net Proceeds		8,509,000	6,147,000
Issuance of Common Stock, Shares		27,676,960	67,080,514
Senior note conversions		987,967	1,039,721
Equity issued in acquisition of noncontrolling interest	1,108,917	1,108,917
Gross Proceeds From Issuance of Common Stock		1,852,771,000	3,681,425,000
Net proceeds from the issuance of common stock		1,792,552,000	3,536,232,000
February 2012 Public Issuance [Member]
Summary of common stock issuances
Public issuance, Shares Issued			20,700,000
Public issuance, Average Price			53.5
Public issuance, Gross Proceeds			1,107,450,000
Public issuance, Net Proceeds			1,062,256,000
August 2012 Public Issuance [Member]
Summary of common stock issuances
Public issuance, Shares Issued			13,800,000
Public issuance, Average Price			58.75
Public issuance, Gross Proceeds			810,750,000
Public issuance, Net Proceeds			778,011,000
September 2012 Public Issuance [Member]
Summary of common stock issuances
Public issuance, Shares Issued			29,900,000
Public issuance, Average Price			56
Public issuance, Gross Proceeds			1,674,400,000
Public issuance, Net Proceeds			1,607,140,000
May 2013 Public Issuance [Member]
Summary of common stock issuances
Public issuance, Shares Issued		23,000,000
Public issuance, Average Price		73.5
Public issuance, Gross Proceeds		1,690,500,000
Public issuance, Net Proceeds		$ 1,630,281,000