Regulatory Matters - Pennsylvania and West Virginia (Details) $ in Thousands					1 Months Ended
	Oct. 19, 2015 USD ($)	Jun. 19, 2015	May. 19, 2015	Oct. 10, 2013 proposal	Apr. 26, 2016 USD ($)	Mar. 31, 2016 USD ($) program
Pennsylvania
Regulatory Matters [Line Items]
Number of requests for proposal | proposal				1
Request for proposal project term				2 years
Pennsylvania | Unfavorable Regulatory Action
Regulatory Matters [Line Items]
Maximum range of possible loss						$ 175,000
Revised implementation plan granted extension period			45 days
Pennsylvania | Three month period
Regulatory Matters [Line Items]
Term of energy contract				3 months
Pennsylvania | Twelve month period
Regulatory Matters [Line Items]
Term of energy contract				12 months
Pennsylvania | Twenty-four month period
Regulatory Matters [Line Items]
Term of energy contract				24 months
Pennsylvania | PPUC
Regulatory Matters [Line Items]
LTIIP recovery period	5 years
Pennsylvania | ME | Subsequent Event
Regulatory Matters [Line Items]
Amount of requested rate increase (decrease)					$ 140,200
Pennsylvania | ME | PPUC
Regulatory Matters [Line Items]
Demand reduction targets proposed return on equity (percent)		1.80%
Energy consumption reduction targets proposed return on equity (percent)		4.00%
Amount of requested rate increase (decrease)	$ 43,440
Pennsylvania | Penn | Subsequent Event
Regulatory Matters [Line Items]
Amount of requested rate increase (decrease)					42,000
Pennsylvania | Penn | PPUC
Regulatory Matters [Line Items]
Demand reduction targets proposed return on equity (percent)		1.70%
Energy consumption reduction targets proposed return on equity (percent)		3.30%
Amount of requested rate increase (decrease)	56,350
Pennsylvania | WP | Subsequent Event
Regulatory Matters [Line Items]
Amount of requested rate increase (decrease)					98,200
Pennsylvania | WP | PPUC
Regulatory Matters [Line Items]
Demand reduction targets proposed return on equity (percent)		1.80%
Energy consumption reduction targets proposed return on equity (percent)		2.60%
Amount of requested rate increase (decrease)	88,340
Pennsylvania | PN | Subsequent Event
Regulatory Matters [Line Items]
Amount of requested rate increase (decrease)					$ 158,800
Pennsylvania | PN | PPUC
Regulatory Matters [Line Items]
Demand reduction targets proposed return on equity (percent)		0.00%
Energy consumption reduction targets proposed return on equity (percent)		3.90%
Amount of requested rate increase (decrease)	$ 56,740
West Virginia | MP and PE | WVPSC
Regulatory Matters [Line Items]
Number of proposed efficient programs | program						3
Energy efficient reduction requirement (percent)						0.50%
Expenditures for cost recovery program						$ 9,900