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.

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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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Contractual interest rate for funds borrowed, under the debt agreement.

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Amount of unamortized debt discount (premium) and debt issuance costs.

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Weighted average interest rate of debt outstanding.

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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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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, 2018	May 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Debt
Debt and capital lease obligations	$ 10,016			$ 9,491
Debt issuance costs, discounts and other	(52)			(56)
Current portion of long-term debt	447			739
Long-term debt, less current portion	9,569			8,752
Revolving Credit Facility [Member]
Debt
Debt and capital lease obligations	44
Credit Facility, aggregate capacity	$ 2,750	$ 2,250
Weighted average interest rate	2.70%
Commercial Paper Program [Member]
Debt
Debt and capital lease obligations	$ 1,053			$ 515
Credit Facility, aggregate capacity	$ 2,750		$ 1,500
Weighted average interest rate	2.40%			1.90%
Canadian Term Loan and Revolving Credit Facility [Member]
Debt
Debt and capital lease obligations				$ 113
Weighted average interest rate				2.50%
Senior Notes, Aggregate [Member]
Debt
Debt and capital lease obligations	$ 6,222			$ 6,222
Weighted average interest rate	4.30%			4.30%
Tax Exempt Bonds [Member]
Debt
Debt and capital lease obligations	$ 2,318			$ 2,370
Current portion of long-term debt	$ 209
Weighted average interest rate	2.20%			2.00%
Capital Leases and Other [Member]
Debt
Debt and capital lease obligations	$ 431			$ 327
Current portion of long-term debt	$ 260
Minimum [Member] \| Senior Notes, Aggregate [Member]
Debt
Interest rate	2.40%
Minimum [Member] \| Tax Exempt Bonds [Member]
Debt
Interest rate	1.35%
Maximum [Member] \| Senior Notes, Aggregate [Member]
Debt
Interest rate	7.75%
Maximum [Member] \| Tax Exempt Bonds [Member]
Debt
Interest rate	4.30%
Maximum [Member] \| Capital Leases and Other [Member]
Debt
Interest rate	12.00%