Components of Net Periodic Benefit Cost (Detail) (USD $) In Millions |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2011 |
Sep. 30, 2010 |
Sep. 30, 2011 |
Sep. 30, 2010 |
|
Pension Benefits |
||||
| Defined Benefit Plan Disclosure [Line Items] | ||||
| Service cost | $ 1.6 | $ 1.8 | $ 4.8 | $ 4.7 |
| Interest cost | 8.6 | 8.7 | 25.8 | 26.1 |
| Expected return on plan assets | (11.6) | (11.1) | (34.9) | (33.3) |
| Amortization of prior service cost | 0.2 | 0.2 | 0.6 | 0.6 |
| Recognized actuarial loss | 3.0 | 2.3 | 9.0 | 6.8 |
| Total net periodic benefit cost | 1.8 | 1.9 | 5.3 | 4.9 |
Other Benefits |
||||
| Defined Benefit Plan Disclosure [Line Items] | ||||
| Service cost | 0.1 | 0.1 | 0.4 | 0.3 |
| Interest cost | 0.4 | 0.4 | 1.2 | 1.3 |
| Expected return on plan assets | (0.4) | (0.3) | (1.2) | (1.1) |
| Amortization of prior service cost | (0.1) | (0.1) | (0.2) | |
| Recognized actuarial loss | 0.3 | 0.3 | 0.9 | 0.9 |
| Total net periodic benefit cost | $ 0.4 | $ 0.4 | $ 1.2 | $ 1.2 |
| X | ||||||||||
- Definition The net increase or decrease of changes in the value of either the benefit obligation or the plan assets resulting from experience different from that assumed or from a change in an actuarial assumption, or the consequence of a decision to temporarily deviate from the substantive plan. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|
| X | ||||||||||
- Definition 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. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|
| X | ||||||||||
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.
|
| X | ||||||||||
- Definition 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. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|
| X | ||||||||||
- Definition 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. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|
| X | ||||||||||
- Definition 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. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|
| X | ||||||||||
- Definition 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. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|