Debt And Credit Arrangements Fair Value Disclosures about Debt (Details)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Debt Instrument, Fair Value Disclosure, Narrative	The fair value of the 2024 Notes was approximately 105% of their par value as of December 31, 2017. The fair value of the 2018 Notes was approximately 99% of their par value as of December 31, 2017 and approximately 96% of their par value as of December 31, 2016. The 2024 Notes and 2018 Notes are actively quoted instruments and, accordingly, the fair values of the 2024 Notes and 2018 Notes were determined using Level 1 inputs as defined in Note 11.