Debt - Components of Debt (Parenthetical) (Detail) - USD ($)	3 Months Ended
Mar. 31, 2016	Dec. 31, 2015
Senior Notes [Member]
Debt Instrument [Line Items]
Weighted average interest rate	4.70%	4.70%
Interest rate lower range	2.60%
Interest rate upper range	7.75%
End period of maturity for debt instrument	Mar. 01, 2045
Tax-exempt Bonds [Member]
Debt Instrument [Line Items]
Weighted average interest rate	2.00%	1.90%
Interest rate lower range	0.40%
Interest rate upper range	5.70%
End period of maturity for debt instrument	Aug. 01, 2045
Capital Leases and Other [Member]
Debt Instrument [Line Items]
Interest rate upper range	12.00%
End period of maturity for debt instrument	Dec. 31, 2055
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Credit Facility, aggregate capacity	$ 2,250,000,000
Weighted average interest rate	1.40%
Maturity date of credit facility	Jul. 30, 2020
Canadian Credit Facility and Term Loan [Member]
Debt Instrument [Line Items]
Weighted average interest rate	2.00%	2.20%
Maturity date of credit facility	Mar. 31, 2019
Standby Letters of Credit [Member]
Debt Instrument [Line Items]
Maturity date of credit facility	Dec. 31, 2018

Maximum contractual interest rate for funds borrowed, under the debt agreement.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Period Type:	duration

- Definition

Minimum contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Latest date the outstanding debt instruments are required to be repaid, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Weighted average interest rate of debt outstanding.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	instant

- Definition

Date the credit facility terminates, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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