Shareholders' Equity (Schedule Of Preferred Stock Outstanding) (Details) - USD ($) $ in Thousands			12 Months Ended
	Oct. 15, 2015	Mar. 14, 2013	Dec. 31, 2015	Dec. 31, 2014
Class of Stock [Line Items]
Shares Outstanding			36,800	39,800
Amount			$ 920,000	$ 995,000
Series S [Member]
Class of Stock [Line Items]
Issuance Date			Jan. 01, 2012	Jan. 01, 2012
Earliest Potential Redemption Date			Jan. 01, 2017	Jan. 01, 2017
Dividend Rate			6.45%	6.45%
Shares Outstanding			9,200	9,200
Amount			$ 230,000	$ 230,000
Series T [Member]
Class of Stock [Line Items]
Issuance Date			May 01, 2012	May 01, 2012
Earliest Potential Redemption Date			May 01, 2017	May 01, 2017
Dividend Rate			6.00%	6.00%
Shares Outstanding			14,000	14,000
Amount			$ 350,000	$ 350,000
Series U [Member]
Class of Stock [Line Items]
Issuance Date			Sep. 01, 2012	Sep. 01, 2012
Earliest Potential Redemption Date			Sep. 01, 2017	Sep. 01, 2017
Dividend Rate			5.75%	5.75%
Shares Outstanding			9,200	9,200
Amount			$ 230,000	$ 230,000
Series V [Member]
Class of Stock [Line Items]
Issuance Date			Mar. 01, 2013	Mar. 01, 2013
Earliest Potential Redemption Date			Mar. 01, 2018	Mar. 01, 2018
Dividend Rate		5.70%	5.70%	5.70%
Shares Outstanding			4,400	4,400
Amount		$ 110,000	$ 110,000	$ 110,000
Series R [Member]
Class of Stock [Line Items]
Issuance Date			Oct. 01, 2010	Oct. 01, 2010
Earliest Potential Redemption Date			Oct. 01, 2015	Oct. 01, 2015
Dividend Rate	6.875%		6.875%	6.875%
Shares Outstanding				3,000
Amount				$ 75,000