Earnings and Dividends per Share (Reconciliation Of Denominator For Basic And Diluted Earnings (Loss) Per Share) (Details) - $ / shares	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings and Dividends Per Share [Abstract]
Weighted average common shares—basic									128,395,184	129,401,823	129,087,043
Weighted Average Number Diluted Shares Outstanding Adjustment									362,109	583,930	452,970
Weighted average common shares—diluted									128,757,293	129,985,753	129,540,013
Basic (in dollars per share)	$ 0.56	$ 1.22	$ 0.92	$ 0.56	$ 0.95	$ 2.36	$ 2.13	$ 2.21	$ 3.26	$ 7.66	$ 10.05
Diluted (in dollars per share)	$ 0.56	$ 1.22	$ 0.92	$ 0.55	$ 0.95	$ 2.35	$ 2.12	$ 2.20	$ 3.25	$ 7.62	$ 10.00