Debt - Additional Information (Detail)			12 Months Ended				12 Months Ended									12 Months Ended			12 Months Ended						12 Months Ended
	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2014 Minimum [Member]	Dec. 31, 2014 Maximum [Member]	Dec. 31, 2014 Nontaxable Municipal Bonds [Member] USD ($)	Dec. 31, 2014 Nontaxable Municipal Bonds [Member] Variable Rate [Member] USD ($)	Dec. 31, 2014 5.0% Senior Notes Due March 2014 [Member] USD ($)	Dec. 31, 2014 3.5% Senior Notes Due May 15 2024 [Member] USD ($)	Dec. 31, 2014 Tax-exempt Bonds [Member] USD ($)	Dec. 31, 2014 6.375% Senior Notes Due March 2015 [Member] USD ($)	Dec. 31, 2014 7.125%t Senior Notes Due December 2017 [Member] USD ($)	Dec. 31, 2014 7.375% Senior Notes Due December 2019 [Member] USD ($)	Dec. 31, 2014 Domestic Line of Credit [Member] USD ($)	Dec. 31, 2013 Domestic Line of Credit [Member] USD ($)	Dec. 31, 2014 Canadian Credit Facility and Term Loan [Member] CAD	Dec. 31, 2014 Canadian Credit Facility and Term Loan [Member] Minimum [Member]	Dec. 31, 2014 Canadian Credit Facility and Term Loan [Member] Maximum [Member]	Dec. 31, 2014 Canadian Credit Facility and Term Loan [Member] Term Loan [Member] CAD	Dec. 31, 2014 U.S. Revolving Credit Facility [Member] USD ($)	Dec. 31, 2014 Letter Of Credit Facilities [Member] USD ($)	Dec. 31, 2014 Canadian Credit Facility [Member] USD ($)	Dec. 31, 2014 Canadian Credit Facility [Member] CAD	Dec. 31, 2013 Canadian Credit Facility [Member] CAD	Dec. 31, 2012 Canadian Credit Facility [Member] CAD	Dec. 31, 2014 Canadian Credit Facility [Member] Term Loan [Member] USD ($)	Dec. 31, 2014 Canadian Credit Facility [Member] Term Loan [Member] CAD	Dec. 31, 2014 Canadian Credit Facility Term Loan [Member] RCI Environnement Inc [Member] CAD
Debt Instrument [Line Items]
Current portion of senior notes	$ 947,000,000									$ 350,000,000	$ 147,000,000	$ 450,000,000
Interest rate of senior notes							5.00%	3.50%		6.375%	7.125%	7.375%
Debt maturing within twelve months	143,000,000
Tax-exempt bonds, current					64,000,000
Tax-exempt bonds subject to re-pricing within next 12 months	638,000,000
Credit Facility, aggregate capacity													2,250,000,000	2,250,000,000	150,000,000			500,000,000		400,000,000		50,000,000		150,000,000			500,000,000
Current debt obligations	1,090,000,000	726,000,000
Debt maturing within twelve months classified as long-term	638,000,000
Variable-rate tax-exempt bonds						501,000,000
Letters of credit outstanding revolving credit facility																			785,000,000			0	0
Credit facility borrowings	0																					0	10,000,000
Spread rate			0.90%	1.475%												1.125%	2.15%
Unused and available credit capacity																			1,465,000,000
Maturity date of credit facility																			Jul. 26, 2018	Dec. 31, 2018
Repayment of credit facility																										230,000,000
Increase (Decrease) in borrowings under credit facility																										270,000,000
Net borrowings (repayments) under credit facility																			420,000,000		9,000,000	10,000,000			155,000,000	170,000,000
Net borrowings (repayments) of senior notes							350,000,000
Debt instrument face amount								350,000,000
Proceeds from debt net of Issuance costs								347,000,000
Repayment of tax exempt bonds									123,000,000
Debt and capital lease principal payments in 2015	1,075,000,000
Debt and capital lease principal payments in 2016	717,000,000
Debt and capital lease principal payments in 2017	402,000,000
Debt and capital lease principal payments in 2018	801,000,000
Debt and capital lease principal payments in 2019	$ 132,000,000