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Acquisitions - Additional Information (Detail) $ in Millions			1 Months Ended		3 Months Ended				11 Months Ended		12 Months Ended
	Jul. 24, 2015 USD ($) extension	Oct. 11, 2013 USD ($) MW	Jul. 31, 2014 USD ($)	Dec. 16, 2013 USD ($)	Jul. 03, 2015 USD ($)	Apr. 03, 2015 USD ($)	Jan. 30, 2015 USD ($)	Nov. 01, 2013 USD ($)	Jan. 01, 2016 USD ($)	Jan. 02, 2015 USD ($)	Jan. 30, 2015 USD ($)	Jan. 31, 2014 USD ($)
Business Acquisition [Line Items]
Receivable due from Plainfield							$ 896		$ 921		$ 896
Interest expense									53	$ 71	75	$ 82
Bad debt expense									8	4	5	44
Proceeds from U.S. Treasury cash grant			$ 80						0	80	80	0
Deferred tax assets			$ 27				311		272		311
Promissory note, net received for disposition of business									$ 72	$ 0	0	$ 0
Plainfield Renewal Energy Holdings LLC
Business Acquisition [Line Items]
Percentage of ownership		100.00%
Capacity of power plant \| MW		37.5
Bad debt expense											32
Contingent consideration		$ 6
Connecticut Light and Power \| Plainfield Renewal Energy Holdings LLC
Business Acquisition [Line Items]
Percentage of power to be purchased		80.00%
Term of agreement		15 years
Plainfield Renewal Energy Holdings LLC
Business Acquisition [Line Items]
Receivable due from Plainfield		$ 137
Carlyle Group \| Plainfield Renewal Energy Holdings LLC
Business Acquisition [Line Items]
Repayment of principal				$ 152
Repayment of debt				165
Interest expense				7
Early termination fees				$ 6
Secured Debt \| Carlyle Group \| Plainfield Renewal Energy Holdings LLC
Business Acquisition [Line Items]
Number of debt instruments financed by Carlyle Grp		2
Senior notes, face amount		$ 148
Receivable from PRE Holdings \| Plainfield Renewal Energy Holdings LLC
Business Acquisition [Line Items]
Bad debt expense								$ 32
Minimum \| Plainfield Renewal Energy Holdings LLC
Business Acquisition [Line Items]
Fuel supply agreement, term		5 years
Maximum \| Plainfield Renewal Energy Holdings LLC
Business Acquisition [Line Items]
Fuel supply agreement, term		15 years
November 2015 or the successful sale of the plant \| Plainfield Renewal Energy Holdings LLC
Business Acquisition [Line Items]
Contingent consideration							2				2
Achievement of Milestones \| Plainfield Renewal Energy Holdings LLC
Business Acquisition [Line Items]
Contingent consideration							3				$ 3
Plainfield Renewal Energy Holdings LLC
Business Acquisition [Line Items]
Asset impairment charges					$ 29	$ 40	$ 40
Discontinued Operations, Held-for-sale \| Plainfield Renewal Energy Holdings LLC
Business Acquisition [Line Items]
Disposal Group, Including Discontinued Operation, Consideration	$ 102
Proceeds from Divestiture of Interest in Consolidated Subsidiaries	29
Promissory note, net received for disposition of business	73
Disposal Group, Including Discontinued Operation, Contingent Consideration, Maximum Earn-out Payment	$ 30
Note Receivable, Option to Extend for One Year Period, Number \| extension	3
Note Receivable, Interest Rate, Stated Percentage	6.00%
Note Receivable, Interest Rate, Stated Percentage, If Maturity is Extended Beyond July Twenty Four Twenty Seventeen	8.00%
Note Receivable, Interest Rate, Stated Percentage, If Maturity is Extended Beyond July Twenty Four Twenty Nineteen	9.00%