Acquisitions (Narrative) (Details) (Plainfield, USD $) In Millions, unless otherwise specified	0 Months Ended
	Oct. 11, 2013 MW
Business Acquisition [Line Items]
Percentage of ownership	100.00%
Capacity of the power plant	37.5
Cash paid for purchase price	$ 111
Forgiveness of accounts receivable (net of $32 million bad debt expense)	$ 105
Minimum
Business Acquisition [Line Items]
Fuel supply agreement, term	5 years
Maximum
Business Acquisition [Line Items]
Fuel supply agreement, term	15 years
Connecticut Light and Power
Business Acquisition [Line Items]
Percentage of power to be purchased	80.00%
Term of agreement	15 years