Benefit Plans (Summary Of Non-Vested Share Award Activity) (Details) - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Non-vested as of December 31, 2011, Shares	2,641
Non-vested Granted, Shares	2,116
Non-vested Vested, Shares	(787)
Non-vested Forfeited, Shares	(827)
Non-vested as of December 31, 2012, Shares	3,143	2,641
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Non-vested as of December 31, 2011, Weighted-Average Grant-Date Fair Value	$ 52.86
Non-vested Granted, Weighted-Average Grant-Date Fair Value	23.95	$ 51.22	$ 59.79
Non-vested Vested, Weighted-Average Grant-Date Fair Value	51.42
Non-vested Forfeited, Weighted-Average Grant-Date Fair Value	41.23
Non-vested as of December 31, 2012, Weighted-Average Grant-Date Fair Value	$ 36.46	$ 52.86