Sum of the carrying values as of the balance sheet date of all debt, including all short-term borrowings, long-term debt, and capital lease obligations.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
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Amount of short-term debt and current maturity of long-term debt and capital lease obligations due within one year or the normal operating cycle, if longer.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Contractual interest rate for funds borrowed, under the debt agreement.

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Weighted average interest rate of debt outstanding.

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- 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.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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-Section S99
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Amount of long-term debt and capital lease obligation due after one year or beyond the normal operating cycle, if longer.

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Debt - Components of Debt (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016	Aug. 31, 2016
Debt
Debt and capital lease obligations	$ 9,345	$ 9,310
Current portion of long-term debt	850	417
Long-term debt, less current portion	8,495	8,893
Revolving Credit Facility [Member]
Debt
Debt and capital lease obligations		426
Credit Facility, aggregate capacity	2,250	$ 2,250
Weighted average interest rate		1.90%
Commercial Paper Program [Member]
Debt
Debt and capital lease obligations	502
Current portion of long-term debt	$ 502
Credit Facility, aggregate capacity			$ 1,500
Weighted average interest rate	1.40%
Canadian Term Loan and Revolving Credit Facility [Member]
Debt
Debt and capital lease obligations	$ 143	$ 239
Weighted average interest rate	2.50%	2.10%
Senior Notes, Aggregate [Member]
Debt
Debt and capital lease obligations	$ 6,033	$ 6,033
Weighted average interest rate	4.60%	4.60%
Tax Exempt Bonds [Member]
Debt
Debt and capital lease obligations	$ 2,339	$ 2,304
Current portion of long-term debt	$ 119
Weighted average interest rate	1.90%	1.80%
Capital Leases and Other [Member]
Debt
Debt and capital lease obligations	$ 328	$ 308
Minimum [Member] \| Senior Notes, Aggregate [Member]
Debt
Interest rate	2.40%	2.40%
Minimum [Member] \| Tax Exempt Bonds [Member]
Debt
Interest rate	1.00%	1.00%
Maximum [Member] \| Senior Notes, Aggregate [Member]
Debt
Interest rate	7.75%	7.75%
Maximum [Member] \| Tax Exempt Bonds [Member]
Debt
Interest rate	5.70%	5.70%
Maximum [Member] \| Capital Leases and Other [Member]
Debt
Interest rate	12.00%