Revenue Recognition (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Reset tariff period for transportation contracts	1 year
Balances previously classified as contract liabilities in prior periods that were recognized as revenues	$ 2,000,000.0	$ 0
Revenues recognized related to performance obligations satisfied or partially satisfied in previous periods	$ 0	$ 0