Segment Disclosures - Segment Earnings From Operations (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jul. 02, 2017	Jul. 03, 2016	Jul. 02, 2017	Jul. 03, 2016
Earnings from Operations
Gross profit	$ 228.8	$ 230.5	$ 460.4	$ 463.2
SG&A expenses	(208.5)	(220.6)	(423.7)	(438.6)
Earnings from operations	20.3	9.9	36.7	24.6
Other Expense, Net	(0.5)	0.0	(2.1)	(0.9)
Earnings before taxes and equity in net earnings (loss) of affiliate	19.8	9.9	34.6	23.7
Less: Intersegment
Earnings from Operations
Gross profit	(0.5)	(1.0)	(1.1)	(2.1)
SG&A expenses	0.5	1.0	1.1	2.1
Earnings from operations	0.0	0.0	0.0	0.0
Corporate
Earnings from Operations
Earnings from operations	(19.5)	(23.6)	(44.8)	(46.3)
Americas Staffing \| Reporting Segments
Earnings from Operations
Gross profit	103.8	97.2	209.1	197.9
SG&A expenses	(83.4)	(81.6)	(167.5)	(165.2)
Earnings from operations	20.4	15.6	41.6	32.7
Global Talent Solutions \| Reporting Segments
Earnings from Operations
Gross profit	88.7	85.7	179.2	171.0
SG&A expenses	(73.4)	(71.8)	(148.6)	(143.4)
Earnings from operations	15.3	13.9	30.6	27.6
International Staffing \| Reporting Segments
Earnings from Operations
Gross profit	36.8	48.6	73.2	96.4
SG&A expenses	(32.7)	(44.6)	(63.9)	(85.8)
Earnings from operations	$ 4.1	$ 4.0	$ 9.3	$ 10.6

Aggregate revenue less cost of goods and services sold or operating expenses directly attributable to the revenue generation activity.

Name:	us-gaap_GrossProfit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of income (loss) from continuing operations before deduction of income tax expense (benefit) and income (loss) attributable to noncontrolling interest, and addition of income (loss) from equity method investments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(h)(1)(i))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

+ Details

Name:	us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The net result for the period of deducting operating expenses from operating revenues.

+ References

No definition available.

+ Details

Name:	us-gaap_OperatingIncomeLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of income (expense) related to nonoperating activities, classified as other.

+ References

+ Details

Name:	us-gaap_OtherNonoperatingIncomeExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- 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.

+ Details

Name:	us-gaap_SegmentReportingReconcilingItemForOperatingProfitLossFromSegmentToConsolidatedLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The aggregate total costs related to selling a firm's product and services, as well as all other general and administrative expenses. Direct selling expenses (for example, credit, warranty, and advertising) are expenses that can be directly linked to the sale of specific products. Indirect selling expenses are expenses that cannot be directly linked to the sale of specific products, for example telephone expenses, Internet, and postal charges. General and administrative expenses include salaries of non-sales personnel, rent, utilities, communication, etc.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.4)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 330
-SubTopic 10
-Section 30
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=68048583&loc=d3e3636-108311

+ Details

Name:	us-gaap_SellingGeneralAndAdministrativeExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_ConsolidationItemsAxis=us-gaap_IntersegmentEliminationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConsolidationItemsAxis=us-gaap_CorporateNonSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=kelya_AmericasStaffingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConsolidationItemsAxis=us-gaap_OperatingSegmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=kelya_GTSMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=kelya_InternationalStaffingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: