Debt and Interest Expense - Interest-Rate Swap Table (Details) - WES Operating [Member] - Not Designated as Hedging Instrument [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Interest-rate swap, notional amount	$ 375	$ 750
Interest-Rate Swap 1 [Member]
Derivative [Line Items]
Interest-rate swap, notional amount	$ 375
Interest-rate swap, reference period start date	Dec. 31, 2019
Interest-rate swap, reference period end date	Dec. 31, 2024
Interest-rate swap, maturity date	Dec. 31, 2019
Interest-rate swap, fixed interest rate	2.662%
Interest-Rate Swap 2 [Member]
Derivative [Line Items]
Interest-rate swap, notional amount	$ 375
Interest-rate swap, reference period start date	Dec. 31, 2019
Interest-rate swap, reference period end date	Dec. 31, 2029
Interest-rate swap, maturity date	Dec. 31, 2019
Interest-rate swap, fixed interest rate	2.802%
Interest-Rate Swap 3 [Member]
Derivative [Line Items]
Interest-rate swap, notional amount	$ 375
Interest-rate swap, reference period start date	Dec. 31, 2019
Interest-rate swap, reference period end date	Dec. 31, 2049
Interest-rate swap, maturity date	Dec. 31, 2019
Interest-rate swap, fixed interest rate	2.885%