Selected Quarterly Financial Data (unaudited) - Schedule of Quarterly Financial Information (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Oct. 01, 2017	Jul. 02, 2017	Apr. 02, 2017	Jan. 01, 2017	Oct. 02, 2016	Jul. 03, 2016	Apr. 03, 2016	Dec. 31, 2017	Jan. 01, 2017	Jan. 03, 2016
Quarterly Financial Information Disclosure [Abstract]
Revenue from services	$ 1,422.3	$ 1,328.8	$ 1,333.6	$ 1,289.7	$ 1,304.4	$ 1,247.8	$ 1,375.5	$ 1,349.1	$ 5,374.4	$ 5,276.8	$ 5,518.2	[1]
Gross profit	263.0	230.7	228.8	231.6	228.0	215.1	230.5	232.7	954.1	906.3	920.3	[1]
SG&A expenses	234.6	212.5	208.5	215.2	208.2	196.3	220.6	218.0	870.8	843.1	853.6	[1]
Restructuring charges included in SG&A expenses	0.0	0.0	0.0	2.4	0.0	0.0	3.4	0.0	2.4	3.4	0.0
Gain on investment in PersolKelly Asia Pacific					0.0	87.2	0.0	0.0	0.0	87.2	0.0	[1]
Net earnings	$ 17.7	$ 23.0	$ 18.7	$ 12.2	$ 19.8	$ 80.9	$ 8.9	$ 11.2	$ 71.6	$ 120.8	$ 53.8	[1]
Basic earnings per share on common stock (in dollars per share)	$ 0.46	$ 0.59	$ 0.48	$ 0.31	$ 0.51	$ 2.08	$ 0.23	$ 0.29	$ 1.84	$ 3.10	$ 1.39	[1]
Diluted earnings per share on common stock (in dollars per share)	0.45	0.58	0.47	0.31	0.51	2.06	0.23	0.29	1.81	3.08	1.39	[1]
Dividends per share (in dollars per share)	$ 0.075	$ 0.075	$ 0.075	$ 0.075	$ 0.075	$ 0.075	$ 0.075	$ 0.05	$ 0.30	$ 0.275	$ 0.20	[1]
Quantifying misstatement in current year financial statements amount		$ 2.8							$ 1.4
Adjustment for amounts determined to be uncollectible					$ 2.8

[1] Fiscal year included 53 weeks.