Stock-based Compensation (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended					9 Months Ended
	Sep. 30, 2013 Restricted Stock Units (RSUs)	Sep. 30, 2012 Restricted Stock Units (RSUs)	Sep. 30, 2013 Restricted Stock Units (RSUs)	Sep. 30, 2012 Restricted Stock Units (RSUs)	Sep. 30, 2013 Jones Lang Lasalle Savings Related Share Option Plan [Member] Options	Sep. 30, 2012 Jones Lang Lasalle Savings Related Share Option Plan [Member] Options	Dec. 31, 2012 Jones Lang Lasalle Savings Related Share Option Plan [Member] Options	Sep. 30, 2013 Three year vesting Jones Lang Lasalle Savings Related Share Option Plan [Member] Options	Sep. 30, 2013 Five year vesting Jones Lang Lasalle Savings Related Share Option Plan [Member] Options
Restricted stock unit activity [Roll Forward]
Unvested at beginning of period (in shares)	1,442,200	1,710,500	1,345,900	1,362,300
Granted (in shares)	58,700	15,600	233,900	592,800
Vested (in shares)	(453,500)	(356,900)	(513,200)	(574,300)
Forfeited (in shares)	(22,000)	(16,200)	(41,200)	(27,800)
Unvested at end of period (in shares)	1,025,400	1,353,000	1,025,400	1,353,000
Unvested shares expected to vest (in shares)	991,100	1,310,900	991,100	1,310,900
Restricted stock unit activity, additional disclosures [Abstract]
Weighted average grant date fair value, beginning of period (in dollars per share)	$ 71.27	$ 68.49	$ 68.50	$ 66.29
Weighted average grant date fair value, granted (in dollars per share)	$ 91.85	$ 70.56	$ 91.33	$ 67.08
Weighted average grant date fair value, vested (in dollars per share)	$ 71.10	$ 69.34	$ 70.82	$ 62.14
Weighted average grant date fair value, forfeited (in dollars per share)	$ 57.56	$ 63.56	$ 61.70	$ 68.70
Weighted average grant date fair value, end of period (in dollars per share)	$ 72.82	$ 68.35	$ 72.82	$ 68.35
Weighted average grant date fair value, unvested shares expected to vest (in dollars per share)	$ 72.94	$ 68.38	$ 72.94	$ 68.38
Weighted average remaining contractual life, unvested shares outstanding and expected to vest	2 years 2 months 27 days	2 years 2 months 19 days	2 years 2 months 27 days	2 years 2 months 19 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable, Weighted Average Remaining Contractual Term	2 years 3 months	2 years 2 months 19 days	2 years 3 months	2 years 2 months 19 days
Unamortized deferred compensation cost	$ 31.7		$ 31.7
Fair value of shares vested	32.2	24.7	36.3	35.7
ShareBased Compensation Arrangement By ShareBased Payment Award, Equity Instruments Other Than Options, Grants In Period, Weighted Average Grant Date Fair Value1	$ 5.4	$ 1.1	$ 21.4	$ 39.8
Other Stock Compensation Programs [Abstract]
Discount on purchase price (in hundredths)					15.00%
Options issued (in shares)					25,400	127,400
Options issued, exercise price (in dollars per share)					$ 77.65	$ 59.26
Options to purchase discounted stock, vesting period (in years)								3 years	5 years
Options outstanding (in shares)					233,000		237,400