Retirement Benefits (Details) (USD $)	12 Months Ended											3 Months Ended		12 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012 North America Pension Plans [Member]	Jun. 30, 2011 North America Pension Plans [Member]	Jun. 30, 2010 North America Pension Plans [Member]	Jun. 30, 2012 Europe Pension Plans [Member]	Jun. 30, 2011 Europe Pension Plans [Member]	Jun. 30, 2010 Europe Pension Plans [Member]	Jun. 30, 2012 Other Postretirement Plans years	Jun. 30, 2011 Other Postretirement Plans	Jun. 30, 2010 Other Postretirement Plans	Jun. 30, 2012 Pension Change In Accounting Principle [Member]	Dec. 31, 2011 Pension Change In Accounting Principle [Member]	Jun. 30, 2012 Pension Change In Accounting Principle [Member]
Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract]
Portion Of Pension And Opeb Plans Represented In Disclosure Portion Disclosed	98.00%
Projected Benefit Obligation Of Pension And Opeb Plans Not Represented In Disclosure	$ 80,900,000
Plan Assets Of Pension And Opeb Plans Not Represented In Disclosure	54,900,000
Net Liability Of Pension And Opeb Plans Not Represented In Disclosure	26,000,000
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Change in accounting method for pension, gross impact													9,500,000	(6,200,000)
Change in accounting method for pension, offset for the period												6,600,000		(3,200,000)
Change in accounting method for pension, tax benefit													3,700,000
Change in accounting method for pension, net of tax													5,800,000
Change in accounting method for pension, impact to OCI													5,800,000
Change in accounting method for pension, Diluted EPS													$ (0.08)
Defined Benefit Plan, Assumptions Used in Calculations [Abstract]
Defined Benefit Plan, Assumptions Used in Calculations, Narrative Description	The following assumptions were used in the valuations of Towers Watson’s defined benefit pension plans. The assumptions presented for the North American plans represent the weighted-average of rates for all U.S. and Canadian plans. The assumptions presented for Towers Watson’s European plans represent the weighted-average of rates for the U.K., Germany and Netherlands plans. In relation to the acquisition of Towers Perrin on January 1, 2010, the legacy plans of Towers Perrin have been included in the assumptions as of and for the years ended June 30, 2010 and 2011.
Assumptions used to determine net periodic benefit cost
Discount Rate (Cost)			5.79%	5.80%	6.43%	5.59%	5.25%	6.03%	5.65%	5.59%	6.53%
Expected long-term rate of return on assets			8.14%	8.16%	8.11%	6.78%	6.79%	6.48%	2.00%	2.00%	2.00%
Rate of increase in compensation levels (Cost)			3.82%	3.88%	3.93%	3.93%	3.88%	5.09%	4.06%	4.07%	3.29%
Assumptions used to determine benefit obligation
Discount Rate (Obligation)			4.86%	5.79%		4.80%	5.62%		4.80%	5.65%
Rate of increase in compensation levels (Obligation)			4.35%	3.82%		3.93%	3.93%		4.50%	4.06%
Assumed health care cost trend rates
Health care cost trend (Cost)									7.61%	8.03%	9.63%
Health care cost trend rate (Obligation)									7.16%	7.61%
Ultimate health care cost trend rate									5.00%
Year that rate reaches ultimate trend rate									2016
Average Remaining Service Period Plan Participants									8
Effect of One-Percentage Point Change in Assumed Health Care Cost Trend Rates
Effect of One Percentage Point Increase on Cost	258,000
Effect of One Percentage Point Decrease on Cost		(212,000)
Effect of One Percentage Point Increase on Obligation	4,280,000
Effect of One Percentage Point Decrease on Obligation		(3,537,000)
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost			61,158,000	58,050,000	38,068,000	10,199,000	12,218,000	9,844,000	2,987,000	4,211,000	3,313,000
Interest cost			141,390,000	139,840,000	95,845,000	38,173,000	39,000,000	30,631,000	10,966,000	11,706,000	8,387,000
Expected return on plan assets			(172,827,000)	(158,708,000)	(93,257,000)	(44,922,000)	(40,420,000)	(27,078,000)	(132,000)	(132,000)	(66,000)
Settlement/(curtailment)			0	4,170,000	2,293,000	4,258,000	(2,323,000)	64,000	0	(2,209,000)	0
Amortization of net loss/(gain)			18,240,000	23,997,000	15,275,000	(3,717,000)	5,574,000	2,615,000	2,206,000	1,674,000	(1,151,000)
Amortization of prior service (credit)/cost			(8,338,000)	(6,632,000)	(1,623,000)	41,000	41,000	41,000	(8,705,000)	(6,842,000)	(571,000)
Other adjustments			9,512,000	868,000	0	545,000	44,000	860,000
Net periodic benefit cost/(income)			49,135,000	61,585,000	56,601,000	4,577,000	14,134,000	16,977,000	7,322,000	8,408,000	9,912,000
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, before Tax, [Abstract]
Current year actuarial loss/(gain)			314,754,000	(172,078,000)		110,377,000	(107,560,000)		(19,357,000)	12,771,000
Amortization of actuarial (loss)/gain			(18,240,000)	(23,997,000)		3,717,000	(5,574,000)		(2,206,000)	(1,674,000)
Current year prior service credit			0	(73,926,000)		0	0		0	(63,745,000)
Amortization of prior service credit/(cost)			8,338,000	6,632,000		(41,000)	(41,000)		8,705,000	6,842,000
Recognition of actuarial gain/(loss) due to settlement/curtailment			0	(4,170,000)		(4,258,000)	2,323,000
Accelerated recognition of prior service credit due to curtailment									0	2,209,000
Other			(13,477,000)	5,378,000		(1,512,000)	4,058,000		(187,000)	(53,000)
Total recognized in other comprehensive loss/(income)			291,375,000	(262,161,000)		108,283,000	(106,794,000)		(13,045,000)	(43,650,000)
Pension and Other Postretirement Benefit Plans, Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year [Abstract]
Actuarial loss			45,608,000			5,865,000			346,000
Prior service (credit)/cost			(8,378,000)			41,000			(8,212,000)
Total			37,230,000			5,906,000			(7,866,000)
Estimated Future Benefit Payments
2013	229,454,000		184,520,000			44,934,000			17,225,000
2014	189,447,000		169,947,000			19,500,000			18,092,000
2015	180,897,000		156,556,000			24,341,000			19,381,000
2016	181,938,000		158,247,000			23,691,000			20,825,000
2017	190,531,000		162,668,000			27,863,000			22,241,000
Years 2018-2022	1,104,591,000		931,636,000			172,955,000			130,861,000
Total expected benefit payments	2,076,858,000		1,763,574,000			313,284,000			228,625,000
Expected Prescription Drug Subsidy Receipts
2013									548,000
2014									355,000
2015									121,000
2016									118,000
2017									114,000
Years 2018-2022									475,000
Total expected retiree drug subsidies									$ 1,731,000