Derivative Financial Instruments (Narrative) (Details)	3 Months Ended	6 Months Ended
	Mar. 31, 2019 USD ($)	Jun. 30, 2019 USD ($) bbl	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Derivative [Line Items]
Debt Instrument, Face Amount		$ 4,447,000,000		$ 4,300,000,000
Net receipt on financial derivatives		8,028,000	$ 0
Good Faith and Margin Deposits with Broker-Dealers		27,533,000		0
Energy commodity derivatives deposits		0		37,328,000
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months		$ (2,400,000)
Energy Related Derivative [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | bbl		30,000
Derivative Liability		$ 12,600,000
Cash Flow Hedging [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Derivative, Notional Amount		100,000,000.0
Cash Flow Hedging [Member] | Interest Rate Contract [Member] | Other Current Liabilities [Member]
Derivative [Line Items]
Derivative Liability		(11,100,000)
4.85% Notes Due 2049 [Member]
Derivative [Line Items]
Debt Instrument, Face Amount	$ 500,000,000.0	$ 500,000,000.0		$ 0
Debt Instrument, Interest Rate, Stated Percentage	4.85%	4.85%
4.85% Notes Due 2049 [Member] | Cash Flow Hedging [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Derivative, Notional Amount	$ 150,000,000.0
Net receipt on financial derivatives	$ (8,000,000.0)