Long-term debt and cash flow hedges - Additional Information (Detail)		3 Months Ended				9 Months Ended
	Jul. 31, 2014 USD ($)	Sep. 30, 2015 USD ($) Derivative	Jun. 30, 2015 USD ($) Derivative	Dec. 31, 2014 USD ($)	Mar. 31, 2011 USD ($) Derivative	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Aug. 31, 2014 USD ($)	Aug. 07, 2014 USD ($)	Aug. 01, 2014 USD ($)	Oct. 31, 2013 USD ($)	Jun. 30, 2008 USD ($)	Jun. 30, 2006 USD ($)
Debt Instrument [Line Items]
Reduction of long-term debt						$ 207,371,000	$ 842,543,000
Rate adjustment to weighted average federal funds rate for credit facility borrowings		0.50%				0.50%
Rate adjustment to one month Eurodollar rate on credit facility borrowings						1.00%
Accounts receivable securitization program credit facility, amount outstanding		$ 300,000,000				$ 300,000,000
Long-term debt		3,009,954,000		$ 3,210,215,000		3,009,954,000
Fair value of debt		$ 3,100,000,000				$ 3,100,000,000
Number of additional forward starting interest rate swaps | Derivative		4
Maturity date of interest rate cash flow hedges					May 31, 2015
Two Point Three Eight Percent Forward Starting Interest Rate Swaps
Debt Instrument [Line Items]
Number of additional forward starting interest rate swaps | Derivative					4
Fixed rate payable on interest rate swap					2.38%
One Point Nine One Percent Forward Starting Interest Rate Swaps
Debt Instrument [Line Items]
Number of additional forward starting interest rate swaps | Derivative					3
Fixed rate payable on interest rate swap					1.91%
One Point Four Zero Percent Forward Starting Interest Rate Swaps
Debt Instrument [Line Items]
Number of additional forward starting interest rate swaps | Derivative			4
Maturity date of interest rate cash flow hedges			Apr. 15, 2019
Fixed rate payable on interest rate swap			1.40%
One Point Two Three Percent Forward Starting Interest Rate Swaps
Debt Instrument [Line Items]
Maturity date of interest rate cash flow hedges		Apr. 15, 2019
Average fixed rate payable on interest rate swap		1.23%				1.23%
Interest Rate Swap
Debt Instrument [Line Items]
Fair value of our interest rate swaps		$ 11,000,000				$ 11,000,000
Fair value of our interest rate swaps, liability		8,000,000		6,000,000		8,000,000
Interest Rate Swap | Other Noncurrent Liabilities
Debt Instrument [Line Items]
Fair value of our interest rate swaps, liability		3,000,000				3,000,000
Cash Flow Hedging
Debt Instrument [Line Items]
Number of additional forward starting interest rate swaps | Derivative					7
Notional amount of interest rate cash flow hedges					$ 825,000,000
Cash Flow Hedging | Two Point Three Eight Percent Forward Starting Interest Rate Swaps
Debt Instrument [Line Items]
Notional amount of interest rate cash flow hedges					600,000,000
Cash Flow Hedging | One Point Nine One Percent Forward Starting Interest Rate Swaps
Debt Instrument [Line Items]
Notional amount of interest rate cash flow hedges					$ 225,000,000
Cash Flow Hedging | One Point Four Zero Percent Forward Starting Interest Rate Swaps
Debt Instrument [Line Items]
Notional amount of interest rate cash flow hedges			$ 500,000,000
Cash Flow Hedging | Forward Starting Interest Rate Swaps
Debt Instrument [Line Items]
Notional amount of interest rate cash flow hedges		400,000,000				400,000,000
Cash Flow Hedging | One Point Two Three Percent Forward Starting Interest Rate Swaps | One Point Two Three Percent Forward Starting Interest Rate Swaps
Debt Instrument [Line Items]
Notional amount of interest rate cash flow hedges		100,000,000				100,000,000
Cash Flow Hedging | One Point Two Three Percent Forward Starting Interest Rate Swaps | One Point Two Three Percent Forward Starting Interest Rate Swaps
Debt Instrument [Line Items]
Notional amount of interest rate cash flow hedges		200,000,000				$ 200,000,000
7.00% Senior Unsecured Notes
Debt Instrument [Line Items]
Reduction of long-term debt	$ 250,000,000
Senior notes, interest rate	7.00%
Debt instrument redemption, date						Jul. 31, 2014
Unsecured notes make-whole redemption price	104.56%
Senior notes, maturity date						Oct. 01, 2018
Write-off deferred charges, original issue discount and make-whole premiums paid	$ 11,000,000
Accounts Receivable Securitization Facility
Debt Instrument [Line Items]
Accounts receivable securitization program, additional capacity		60,000,000				$ 60,000,000
Senior Notes 7.125%
Debt Instrument [Line Items]
Senior notes, interest rate													7.125%
Senior notes, issued													$ 250,000,000
Senior notes, maturity date						Jun. 30, 2016
Senior notes, repayment terms						Interest on the 7.125% Notes is payable semiannually in arrears on June 30th and December 30th of each year.
Line of credit facility additional borrowing capacity												$ 150,000,000
Amendment of Credit Facility
Debt Instrument [Line Items]
Line of credit facility, starting date						Aug. 07, 2014
Line of credit facility, maturity						2019-08
Accounts receivable securitization program credit facility, borrowing capacity										$ 360,000,000	$ 275,000,000
Amendment of Credit Facility | Accounts Receivable Securitization Facility
Debt Instrument [Line Items]
Line of credit facility, starting date						Aug. 01, 2014
Line of credit facility, maturity						2016-10
Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit facility, borrowing capacity		800,000,000				$ 800,000,000		$ 800,000,000
Line of credit facility amount outstanding		$ 0				$ 0
Current applicable margins		1.50%				1.50%
Line of credit facility, available borrowing capacity		$ 744,000,000				$ 744,000,000
Letters of credit, outstanding		39,000,000				39,000,000
Revolving Credit Facility | Short Term on Demand Credit Facility
Debt Instrument [Line Items]
Line of credit facility amount outstanding		17,000,000				17,000,000
Revolving Credit Facility | Letter of Credit
Debt Instrument [Line Items]
Line of credit facility, borrowing capacity		$ 125,000,000				$ 125,000,000
Revolving Credit Facility | ABR-based loans
Debt Instrument [Line Items]
Current applicable margins		0.50%				0.50%
Revolving Credit Facility | Minimum | One Month Eurodollar Rate Plus Index Based Loans
Debt Instrument [Line Items]
Consolidated leverage ratio		0.50%				0.50%
Revolving Credit Facility | Minimum | One Two Three Six Month Eurodollar Rate Plus Index Based Loans
Debt Instrument [Line Items]
Consolidated leverage ratio		1.50%				1.50%
Revolving Credit Facility | Maximum | One Month Eurodollar Rate Plus Index Based Loans
Debt Instrument [Line Items]
Consolidated leverage ratio		1.25%				1.25%
Revolving Credit Facility | Maximum | One Two Three Six Month Eurodollar Rate Plus Index Based Loans
Debt Instrument [Line Items]
Consolidated leverage ratio		2.25%				2.25%
Term Loan A
Debt Instrument [Line Items]
Current applicable margins		1.50%				1.50%
Term Loan A | ABR-based loans
Debt Instrument [Line Items]
Current applicable margins		0.50%				0.50%
Term Loan A | Minimum | One Month Eurodollar Rate Plus Index Based Loans
Debt Instrument [Line Items]
Consolidated leverage ratio		0.50%				0.50%
Term Loan A | Minimum | One Two Three Six Month Eurodollar Rate Plus Index Based Loans
Debt Instrument [Line Items]
Consolidated leverage ratio		1.50%				1.50%
Term Loan A | Maximum | One Month Eurodollar Rate Plus Index Based Loans
Debt Instrument [Line Items]
Consolidated leverage ratio		1.25%				1.25%
Term Loan A | Maximum | One Two Three Six Month Eurodollar Rate Plus Index Based Loans
Debt Instrument [Line Items]
Consolidated leverage ratio		2.25%				2.25%
Term Loan A | Quarterly installment payments commence in the fourth quarter of 2014 through September, 2016
Debt Instrument [Line Items]
Scheduled principal payments made				11,000,000
Term Loan A | Quarterly installment payments after September, 2016
Debt Instrument [Line Items]
Scheduled principal payments made				$ 22,000,000
Term Loan A | Amendment of Credit Facility
Debt Instrument [Line Items]
Line of credit facility, borrowing capacity								$ 1,775,000,000
Line of credit facility amount outstanding		$ 1,731,000,000				$ 1,731,000,000
Term Loan B Facility
Debt Instrument [Line Items]
Reduction of long-term debt						$ 550,000,000
Line of credit facility, maturity year						2016
New Senior Secured Notes | 3.750% Senior Secured Notes due 2019
Debt Instrument [Line Items]
Senior notes, interest rate									3.75%
Senior notes, issued									$ 300,000,000
Senior notes, maturity date						Aug. 01, 2019
Senior notes, interest payment, commencement date						Feb. 01, 2015
New Senior Secured Notes | 4.750% Senior Secured Notes due 2022
Debt Instrument [Line Items]
Senior notes, interest rate									4.75%
Senior notes, issued									$ 300,000,000
Senior notes, maturity date						Aug. 01, 2022