Defined Benefit Pension and Other Postretirement Plans (Details) (USD $) In Millions	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended
Dec. 31, 2010	Jun. 30, 2011 Pension Benefit [Member]	Jun. 30, 2010 Pension Benefit [Member]	Jun. 30, 2011 Pension Benefit [Member]	Jun. 30, 2010 Pension Benefit [Member]	Jun. 30, 2011 Other Postretirement Benefits [Member]	Jun. 30, 2010 Other Postretirement Benefits [Member]	Jun. 30, 2011 Other Postretirement Benefits [Member]	Jun. 30, 2010 Other Postretirement Benefits [Member]
Components of net periodic pension expense and other postretirement benefit costs
Service cost	$ 2.2	$ 2.1	$ 2.2	$ 6.6	$ 6.5	$ 0.1	$ 0.1	$ 0.4	$ 0.3
Interest cost	5.8	6.1	5.8	18.1	17.6	0.3	0.3	0.8	0.9
Expected return on assets		(6.4)	(6.5)	(19.4)	(19.4)	(0.1)	(0.1)	(0.4)	(0.3)
Amortization of:
Prior service cost (benefit)		0.1		0.2		(0.2)	(0.1)	(0.5)	(0.3)
Actuarial loss		1.7	1.5	5.7	4.4	0.1	0.1	0.3	0.2
Net benefit cost		3.6	3.0	11.2	9.1	0.2	0.3	0.6	0.8
Change in associated regulatory liabilities						0.8	0.7	2.4	2.2
Net expense		$ 3.6	$ 3.0	$ 11.2	$ 9.1	$ 1.0	$ 1.0	$ 3.0	$ 3.0

Net Periodic Benefit Cost After Change in regulatory liabilities.

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The amount of gains or losses recognized in net periodic benefit cost.

+ References

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The amount of the prior service cost or credit recognized in net periodic benefit cost relating to benefit changes attributable to plan participants' prior service pursuant to a plan amendment or a plan initiation.

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An amount calculated as a basis for determining the extent of delayed recognition of the effects of changes in the fair value of assets. The expected return on plan assets is determined based on the expected long-term rate of return on plan assets and the market-related value of plan assets.

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The increase in a defined benefit pension plan's projected benefit obligation or a defined benefit postretirement plan's accumulated postretirement benefit obligation due to the passage of time.

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The total amount of net periodic benefit cost for defined benefit plans for the period. Periodic benefit costs include the following components: service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) due to settlements or curtailments.

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The actuarial present value of benefits attributed by the pension benefit formula to services rendered by employees during the period. The portion of the expected postretirement benefit obligation attributed to employee service during the period. The service cost component is a portion of the benefit obligation and is unaffected by the funded status of the plan.

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The increase (decrease) during the reporting period in regulated liabilities. Regulated liabilities are created when regulatory agency permits an entity to defer revenues to the balance sheet.

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