Share-Based Compensation (Details1) (USD $)	12 Months Ended
	Jun. 30, 2012 years	Jun. 30, 2011 years	Jun. 30, 2010 years	Jun. 30, 2012
Stock Options Explanatory Disclosures
Options granted previously and assumed in a business acquiree	377,614
Number of options granted	378,000		234,581
Compensation expense	$ 54,500,000	$ 78,000,000	$ 57,900,000
Weighted-average grant date fair value of options granted	$ 52.70		$ 11.02
Stock option assumptions
Postvesting restriction discount			1.40%
Risk-free interest rate	0.33%		1.40%
Expected lives in years	2.2		3
Expected volatility	38.50%		37.20%
Dividend yield	0.60%		0.60%
Weighted-average grant date fair value of options granted	$ 52.70		$ 11.02
Number of shares granted	378,000		234,581
Stock options activity rollforward, shares
Outstanding as at, shares	188,000	235,000
Granted	378,000		234,581
Exercised	(17,000)	(47,000)
Outstanding as at, shares	549,000	188,000	235,000
Stock options activity rollforward, weighted average exercise price
Balance as at, weighted average exercise price	$ 44.11	$ 44.05		$ 19.42
Granted	$ 8.27
Exercised	$ (43.44)	$ (43.83)
Stock options activity, additional disclosures
Intrinsic Value of exercised options	273,000	425,000
Intrinsic Value of Outstanding Options	22,172,000	4,052,000
Average remaining contractual term, outstanding options	7.2	6.4	5.5
Average remaining contractual term, granted options	8.3
Stock options outstanding and exercisable
Number of shares, outstanding	547,776
Weighted average exercise price, outstanding	$ 19.43
Number of shares, exercisable	170,162
Weighted average exercise price, outstanding	$ 44.18
$0.75 - $1.55
Stock options outstanding and exercisable
Lower range of exercise prices	$ 0.75
Upper range of exercise prices	$ 1.55
Number of shares, outstanding	70,262
Remaining contractual life, outstanding	1.2
Weighted average exercise price, outstanding	$ 1.33
$3.31 - $3.97
Stock options outstanding and exercisable
Lower range of exercise prices	$ 3.31
Upper range of exercise prices	$ 3.97
Number of shares, outstanding	183,861
Remaining contractual life, outstanding	2.0
Weighted average exercise price, outstanding	$ 3.39
$19.21 - $25.18
Stock options outstanding and exercisable
Lower range of exercise prices	$ 19.21
Upper range of exercise prices	$ 25.18
Number of shares, outstanding	123,491
Remaining contractual life, outstanding	3.1
Weighted average exercise price, outstanding	$ 19.49
$42.47
Stock options outstanding and exercisable
Number of shares, outstanding	84,945			84,945
Remaining contractual life, outstanding	4.5			4.5
Weighted average exercise price, outstanding	$ 42.47			$ 42.47
Number of shares, exercisable	84,945			84,945
Remaining contractual life, exercisable	4.5			4.5
Weighted average exercise price, outstanding	$ 42.47			$ 42.47
$45.88
Stock options outstanding and exercisable
Number of shares, outstanding	85,217			85,217
Remaining contractual life, outstanding	4.7			4.7
Weighted average exercise price, outstanding	$ 45.88			$ 45.88
Number of shares, exercisable	85,217			85,217
Remaining contractual life, exercisable	4.7			4.7
Weighted average exercise price, outstanding	$ 45.88			$ 45.88
Extend Health Vested Options [Member]
Stock Options Explanatory Disclosures
Options granted previously and assumed in a business acquiree	199,620
Compensation expense	11,200,000
Extend Health Unvested Options [Member]
Stock Options Explanatory Disclosures
Options granted previously and assumed in a business acquiree	177,994
Compensation expense	7,900,000
Forfeiture rate	10.00%
Extend Health Accelerated Options [Member]
Stock Options Explanatory Disclosures
Options granted previously and assumed in a business acquiree	43,317
Compensation expense	900,000
Towers Watson Long Term Incentive Plan [Member]
Stock Options Explanatory Disclosures
Number of options granted			108,933
Compensation expense			1,300,000
Weighted-average grant date fair value of options granted			$ 45.88
Stock option assumptions
Weighted-average grant date fair value of options granted			$ 45.88
Number of shares granted			108,933
Stock options activity rollforward, shares
Granted			108,933
Watson Wyatt Long Term Incentive Plan [Member]
Stock Options Explanatory Disclosures
Number of options granted			125,648
Compensation expense			$ 1,300,000
Weighted-average grant date fair value of options granted			$ 42.47
Stock option assumptions
Weighted-average grant date fair value of options granted			$ 42.47
Number of shares granted			125,648
Stock options activity rollforward, shares
Granted			125,648