Debt - Components of Debt (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Debt
Debt	$ 13,358	$ 10,026
Debt issuance costs, discounts and other	(85)	(52)
Current portion of long-term debt	211	432
Long-term debt, less current portion	13,147	9,594
Revolving Credit Facility [Member]
Debt
Debt		$ 11
Weighted average interest rate		3.10%
Commercial Paper Program [Member]
Debt
Debt		$ 990
Weighted average interest rate		2.90%
Senior Notes, Aggregate [Member]
Debt
Debt	$ 9,965	$ 6,222
Weighted average interest rate	3.90%	4.30%
Canadian Senior Notes [Member]
Debt
Debt	$ 377
Interest rate (as a percent)	2.60%
Tax Exempt Bonds [Member]
Debt
Debt	$ 2,409	$ 2,388
Current portion of long-term debt	$ 124
Weighted average interest rate	2.30%	2.35%
Financing leases and other [Member]
Debt
Debt	$ 692	$ 467
Current portion of long-term debt	$ 211
Minimum [Member] \| Senior Notes, Aggregate [Member]
Debt
Interest rate (as a percent)	2.40%
Minimum [Member] \| Tax Exempt Bonds [Member]
Debt
Interest rate (as a percent)	1.35%
Maximum [Member] \| Senior Notes, Aggregate [Member]
Debt
Interest rate (as a percent)	7.75%
Maximum [Member] \| Tax Exempt Bonds [Member]
Debt
Interest rate (as a percent)	4.30%
Maximum [Member] \| Financing leases and other [Member]
Debt
Interest rate (as a percent)	9.00%

Amount of short-term and long-term debt and lease obligation.

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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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- Definition

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

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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.

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

Weighted average interest rate of debt outstanding.

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- Definition

Amount of long-term debt and lease obligation, classified as noncurrent.

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