Shareholders' Equity (Summary Of Preferred Stock) (Details) - USD ($) $ in Thousands		12 Months Ended
	Dec. 31, 2015	Dec. 31, 2016
Schedule of Equity Method Investments [Line Items]
Common Stock Held in Trust	$ 15,200	$ 14,100
Preferred stock, authorized shares	4,400,000	4,400,000
Carrying value, Preferred stock	$ 828,490	$ 709,601
Series A Preferred Stock [Member]
Schedule of Equity Method Investments [Line Items]
Rate		> of 4.0% or 3mL+0.52%
Earliest redemption date		Dec. 15, 2011
Preferred stock, authorized shares		140,000,000
Outstanding Shares at December 31, 2012		66,139,000
Carrying value, Preferred stock	66,316	$ 66,316
Series F Preferred Stock [Member]
Schedule of Equity Method Investments [Line Items]
Earliest redemption date		Jun. 15, 2017
Preferred stock, authorized shares		250,000,000
Outstanding Shares at December 31, 2012		143,750,000
Carrying value, Preferred stock	$ 143,750	$ 143,750
Preferred Stock, Dividend Rate, Percentage		7.90%
Series G Preferred Stock [Member]
Schedule of Equity Method Investments [Line Items]
Interest rate following earliest redemption date	3mL+4.24%
Earliest redemption date		Mar. 15, 2023
Preferred stock, authorized shares		200,000,000
Outstanding Shares at December 31, 2012		138,391,000
Carrying value, Preferred stock	$ 171,827	$ 138,391
Preferred Stock, Dividend Rate, Percentage		6.30%
Series H Preferred Stock [Member]
Schedule of Equity Method Investments [Line Items]
Earliest redemption date		Jun. 15, 2019
Preferred stock, authorized shares		126,221,000
Outstanding Shares at December 31, 2012		126,221,000
Carrying value, Preferred stock	$ 126,221	$ 126,221
Preferred Stock, Dividend Rate, Percentage		5.75%
Series I Preferred Stock [Member]
Schedule of Equity Method Investments [Line Items]
Interest rate following earliest redemption date	3mL+3.80%
Earliest redemption date		Jun. 15, 2023
Preferred stock, authorized shares		300,893,000
Outstanding Shares at December 31, 2012		98,555,000
Carrying value, Preferred stock	$ 125,224	$ 98,555
Preferred Stock, Dividend Rate, Percentage		5.80%
Series J Preferred Stock [Member]
Schedule of Equity Method Investments [Line Items]
Interest rate following earliest redemption date	3mL+4.44%
Earliest redemption date		Sep. 15, 2023
Preferred stock, authorized shares		195,152,000
Outstanding Shares at December 31, 2012		136,368,000
Carrying value, Preferred stock	$ 195,152	$ 136,368
Preferred Stock, Dividend Rate, Percentage		7.20%