Recently Issued Accounting Pronouncements (Details)	9 Months Ended
	Sep. 30, 2016
Accounting Standards Update 2016-15 [Member]
Recently Issued Accounting Pronouncements [Line Items]
Accounting pronouncement description	This ASU has several amendments, which are designed to reduce existing diversity in practice of how certain cash receipts and cash payments are presented and classified in the statement of cash flows. The ASU addresses eight specific cash flow issues, of which the following are expected to be applicable to Swift: 1) debt prepayment and extinguishment costs, 2) proceeds from settlement of insurance claims, 3) proceeds from settlement of corporate-owned life insurance policies, 4) beneficial interests in securitization transactions, and 5) separately identifiable cash flows and application of the predominance principle.
Adoption date and method	January 2018, Retrospective
Financial statement impact	Currently under evaluation; not expected to be material.
Accounting Standards Update 2016-13 [Member]
Recently Issued Accounting Pronouncements [Line Items]
Accounting pronouncement description	The purpose of this ASU is to amend the current incurred loss impairment methodology with a new methodology that reflects expected credit losses and requires a broader range of reasonable and supportable information to inform credit loss estimates. This is the final credit accounting standard, out of a series, with detailed guidance on the new loss reserve model, Current Expected Credit Loss ("CECL"). Among other provisions, the amendments in the ASU require a financial asset (or group of assets) measured at amortized cost basis to be presented at the net amount expected to be collected. Entities are no longer required to wait until a loss is probable to record it.
Adoption date and method	January 2020, Adoption method varies by amendment
Financial statement impact	Currently under evaluation; not expected to be material.
Accounting Standards Update 2016-12 [Member]
Recently Issued Accounting Pronouncements [Line Items]
Accounting pronouncement description	The amendments in this ASU clarify certain aspects regarding the collectibility criterion, sales taxes collected from customers, noncash consideration, contract modifications, and completed contracts at transition. It additionally clarifies that retrospective application only requires disclosure of the accounting change effect on prior periods presented, not on the period of adoption.
Adoption date and method	January 2018, Modified retrospective
Financial statement impact	Impact of ASC Topic 606 overall is currently under evaluation; may be material, but not yet quantifiable.
Accounting Standards Update 2016-10 [Member]
Recently Issued Accounting Pronouncements [Line Items]
Accounting pronouncement description	The amendments in this ASU clarify the following two aspects of Topic 606: identifying performance obligations and the licensing implementation guidance, while retaining the related principles for those areas. The amendments do not change the core principle of the guidance.
Adoption date and method	January 2018, Modified retrospective
Financial statement impact	Impact of ASC Topic 606 overall is currently under evaluation; may be material, but not yet quantifiable.
Accounting Standards Update 2016-08 [Member]
Recently Issued Accounting Pronouncements [Line Items]
Accounting pronouncement description	The amendments in this ASU are intended to improve the operability and understandability of the implementation guidance on principal versus agent considerations, but do not change the core principle of the guidance.
Adoption date and method	January 2018, Modified retrospective
Financial statement impact	Impact of ASC Topic 606 overall is currently under evaluation; may be material, but not yet quantifiable.
Accounting Standards Update 2016-09 [Member]
Recently Issued Accounting Pronouncements [Line Items]
Accounting pronouncement description	The amendments in this ASU are intended to simplify various aspects of accounting for stock-based compensation, including income tax consequences, classification of awards as equity or liability, as well as classification of activities within the statement of cash flows.
Adoption date and method	January 2017, Adoption method varies by amendment
Financial statement impact	Currently under evaluation; not yet quantifiable.
Accounting Standards Update 2016-02 [Member]
Recently Issued Accounting Pronouncements [Line Items]
Accounting pronouncement description	The new standard requires lessees to recognize assets and liabilities arising from both operating and financing leases on the balance sheet. Lessor accounting for leases is largely unaffected by the new guidance.
Adoption date and method	January 2019, Modified retrospective
Financial statement impact	Currently under evaluation; expected to be material, but not yet quantifiable.
Accounting Standards Update 2016-01 [Member]
Recently Issued Accounting Pronouncements [Line Items]
Accounting pronouncement description	The amendments in this ASU address various aspects of recognition, measurement, presentation, and disclosure of financial instruments. They additionally establish ASC Topic 321 – Investments – Equity Securities, which applies to investments in equity securities and other ownership interests in an entity, including investments in partnerships, unincorporated joint ventures, and limited liability companies.
Adoption date and method	January 2018, Modified retrospective
Financial statement impact	Not expected to be material.