Risk Management and Hedging Activities - Additional Information (Details) gal in Millions, $ in Billions	9 Months Ended
Sep. 30, 2016 USD ($) gal
Pay Floating Receive Fixed Swaps
Derivative [Line Items]
Notional principal amount of interest rate swaps \| $	$ 2
Commodity Derivatives
Derivative [Line Items]
Underlying, Derivative Volume \| gal	0

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

Name:	invest_DerivativeNotionalAmount
Namespace Prefix:	invest_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant