Senior Notes (Schedule Of Outstanding Senior Notes) (Details) (Senior Notes [Member], USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
4.868% Senior notes due 6/1/2044 [Member]
Debt Instrument [Line Items]
Debt instrument, stated interest rate	4.868%	0.00%
Date issued	Jun. 05, 2014
Date due	Jun. 01, 2044	Jun. 01, 2044
Principal amounts	$ 400,000,000
Consolidated balance sheet amount	400,000,000
Market value	404,892,000
5.4% Senior notes due 10/15/2014 [Member]
Debt Instrument [Line Items]
Debt instrument, stated interest rate	5.40%	5.40%
Date issued	Oct. 12, 2004
Date due	Oct. 15, 2014	Oct. 15, 2014
Principal amounts	250,000,000
Consolidated balance sheet amount		249,958,000
Market value		259,130,000