Pension Plans (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Plan net pension (credit)/charge:
Total	$ (0.3)	$ 0.5	$ 10.8
UK Plan [Member]
Plan net pension (credit)/charge:
Service cost	1.6	1.6	1.6
Interest cost on PBO	32.2	36.6	40.8
Expected return on plan assets	(34.1)	(36.7)	(35.9)
Amortization of prior service credit	(1.3)	(1.3)	(0.9)
Amortization of actuarial net losses	1.3	0.3	5.2
Total	$ (0.3)	$ 0.5	$ 10.8
Plan assumptions (%):
Discount rate	4.15%	4.75%	5.40%
Inflation rate	2.20%	2.15%	2.80%
Rate of increase in compensation levels	0.00%	0.00%	0.00%
Rate of return on plan assets	4.90%	4.85%	5.45%
Plan asset allocation by category (%):
Total plan asset allocation by category	100.00%	100.00%	100.00%
UK Plan [Member] \| Equity securities [Member]
Plan assumptions (%):
Rate of return on plan assets	7.25%	7.70%	7.70%
Plan asset allocation by category (%):
Total plan asset allocation by category	31.00%	29.00%	27.00%
UK Plan [Member] \| Debt securities [Member]
Plan assumptions (%):
Rate of return on plan assets	3.65%	3.60%	4.50%
Plan asset allocation by category (%):
Total plan asset allocation by category	63.00%	66.00%	73.00%
UK Plan [Member] \| Cash [Member]
Plan asset allocation by category (%):
Total plan asset allocation by category	6.00%	5.00%	0.00%

Defined benefit plan assumptions used calculating net periodic benefit cost inflation rate.

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- Definition

The amounts in accumulated other comprehensive income related to gains and losses that are not recognized immediately and are expected to be recognized as components of net periodic benefit cost over the next fiscal year that follows the most recent annual statement of financial position presented.

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- 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.

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The interest rate used to adjust for the time value of money.

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- Definition

An assumption as to the rate of return on plan assets reflecting the average rate of earnings expected on the funds invested or to be invested to provide for the benefits included in the benefit obligation.

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-Glossary Expected Long-Term Rate of Return on Plan Assets

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- Definition

Expected rate of compensation increases (for pay-related plans).

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- 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.

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- 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.

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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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-Glossary Service Cost (Component of Net Periodic Pension Cost)

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Target allocation of investments of this type to total plan assets presented on a weighted average basis.

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