Other Material Contingencies - Additional Information (Detail)		1 Months Ended	12 Months Ended
	Mar. 12, 2014 People building	Jul. 31, 2007 Person	Dec. 31, 2015 USD ($) Lawsuits	Dec. 31, 2014 USD ($)
Guarantor Obligations [Line Items]
Number of people who died in stream rupture incident | Person		1
Number of suits pending against the company | Lawsuits			90
Estimated accrued liability for suits			$ 50,000,000
Insurance receivable for suits			50,000,000
Number of buildings destroyed by fire | building	2
Number of people who died in explosion or fire incident | People	8
Number of people injured in explosion and fire incident (more than) | People	50
Guarantee obligations maximum exposure			$ 2,856,000,000	$ 2,547,000,000
Ownership interest, percentage			45.70%
Estimated project cost percentage			175.00%
Manhattan Explosion and Fire
Guarantor Obligations [Line Items]
Number of suits pending against the company | Lawsuits			70
Other
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure			$ 75,000,000
Indemnity agreements amount			70,000,000
Electric provider obligation to Public Utility Commission of Texas			$ 5,000,000