Employee Share-Based Incentive Compensation Plans (WTM - Performance Shares) (Details) (USD $) In Millions, except Share data, unless otherwise specified			3 Months Ended						9 Months Ended	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 WTM Incentive Plan and WTM Phantom Share Plans Performance Share		Mar. 31, 2012 WTM Incentive Plan and WTM Phantom Share Plans Performance Share		Mar. 31, 2013 Performance Cycle 2010 to 2012 WTM Incentive Plan and WTM Phantom Share Plans Performance Share	Mar. 31, 2013 WTM Incentive Plan and WTM Phantom Share Plans Performance Share	Sep. 30, 2012 Performance cycle 2009-2011 Performance Share	Mar. 31, 2012 Performance cycle 2009-2011 WTM Incentive Plan and WTM Phantom Share Plans Performance Share
Target Performance Share activity
Beginning of period (in shares)			119,357		150,064
Shares paid or expired (in shares)			(47,310)	[1]	(68,357)	[1]
New grants (in shares)			46,920		35,932
Assumed forfeitures and cancellations			9	[2]	811	[2]
Ending of period (in shares)			118,976		118,450
Accrued Expense
Accrued expense at the beginning of period	$ 100.8	$ 159.0	$ 29.4		$ 66.1
Payments and deferrals			(11.0)	[1]	(48.4)	[1]
Assumed forfeitures and cancellations			0.1	[2]	1.0	[2]
Expense recognized			10.1		8.7
Accrued expense at the end of the period	100.8	159.0	28.6		27.4
Vesting Period								3 years
Percentage of payout for minimum growth target percentage							33.00%			147.00%
Percentage of payout for maximum growth target percentage							98.00%			155.00%
Vested (in shares)									9,577
Additional compensation cost that would be recognized if all outstanding performance shares vested			$ 44.4

[1] WTM performance share payments in 2013 for the 2010-2012 performance cycle ranged from 33% to 98% of target. WTM performance share payments in 2012 for the 2009-2011 performance cycle ranged from 147% to 155% of target.

[2] Amounts include changes in assumed forfeitures, as required under GAAP.