Fuel, Materials and Supplies and Allowance Inventory (Details) (Public Service Company Of New Hampshire [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012 Emission Allowances [Member]	Dec. 31, 2011 Emission Allowances [Member]	Dec. 31, 2013 Emission Allowances [Member]
Other Inventory, Capitalized Costs		$ 0.4		$ 0.2
Other Inventory, Noncurrent		19.4		19.4
Amortization of Power Contracts Emission Credits	0.3	0.4	5.1
EmissionAllowanceAuctionProceeds	$ 6.8