Commitments, Contingencies and Legal Proceedings - Additional Information (Detail) (USD $)	0 Months Ended	3 Months Ended	0 Months Ended		1 Months Ended
	Oct. 14, 2014	Mar. 31, 2015 Operable_Unit	Apr. 09, 2015	Sep. 25, 2014	Jan. 31, 2008
Commitments Contingencies And Litigation [Line Items]
Number of operable units		5
Upper end estimate of total past and future response costs	$ 1,100,000,000
Uncertainty premium for future response costs	100,000,000
Initial minimum amount of NRD assessment		176,000,000
Initial maximum amount of NRD assessment		333,000,000
Revised minimum amount of NRD assessment		287,000,000
Revised maximum amount of NRD assessment		423,000,000
Natural resource damage compensation by settling parties	45,900,000
Total amount recovered by governments for natural resource damages	105,000,000
Other prepaid loss contingencies for earlier settlements	59,000,000
Cost of response incurred by government		4,280,000
Reserve for Environmental liabilities, current portion		5,000,000
Total reserves for site		16,200,000
Maximum estimated percentage of discharge		27.00%
Maximum estimated cost related to Fox River matter		185,000,000
Subsequent Event [Member] | Whiting Litigation [Member]
Commitments Contingencies And Litigation [Line Items]
Remaining costs and damages amount			33,000,000
Subsequent Event [Member] | Whiting Litigation [Member] | NCR and GP [Member]
Commitments Contingencies And Litigation [Line Items]
Costs and damages amount			67,000,000
Maximum [Member]
Commitments Contingencies And Litigation [Line Items]
Period over which estimated cost to be incurred		3 years
Minimum [Member]
Commitments Contingencies And Litigation [Line Items]
Period over which estimated cost to be incurred		2 years
OU1 [Member]
Commitments Contingencies And Litigation [Line Items]
Estimated future cost of work yet to be done	100,000,000
OU2-5 [Member]
Commitments Contingencies And Litigation [Line Items]
Estimated future cost of work yet to be done	500,000,000
Annual estimated cost rate seek by Government		70,000,000
NCR costs and damages percentage				100.00%
OU2-5 [Member] | Whiting Litigation [Member]
Commitments Contingencies And Litigation [Line Items]
NCR costs and damages percentage					100.00%
OU2-5 [Member] | Subsequent Event [Member]
Commitments Contingencies And Litigation [Line Items]
Annual estimated cost rate seek by Government			100,000,000
Dredging Season [Member]
Commitments Contingencies And Litigation [Line Items]
Annual estimated cost rate seek by Government		$ 100,000,000