Risk Management (Notional Amounts and Terms of Company's Derivative Financial Instruments) (Details) bcf in Millions, MMBbls in Millions	Sep. 30, 2021 bcf MMBbls	Dec. 31, 2020 MMBbls bcf
Propane, ethane, butane, heating oil and crude oil (MMBbls) | Fixed Price Payor
Derivative [Line Items]
Derivative, notional amount | MMBbls	73.9	72.7
Propane, ethane, butane, heating oil and crude oil (MMBbls) | Fixed Price Receiver
Derivative [Line Items]
Derivative, notional amount | MMBbls	78.4	76.5
Natural gas (Bcf) | Fixed Price Payor
Derivative [Line Items]
Derivative, notional amount | bcf	32.1	22.6
Natural gas (Bcf) | Fixed Price Receiver
Derivative [Line Items]
Derivative, notional amount | bcf	42.8	28.6