Retirement Benefit Plans (Schedule of fair value of plan assets by three level fair value hierarchy) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Defined benefit plan, fair value of plan assets	$ 294.6	$ 288.3
Cash and Cash Equivalents [Member]
Defined benefit plan, fair value of plan assets	0.2	0.3
Fund Investments [Member]
Defined benefit plan, fair value of plan assets	134.1	140.5
Equity securities [Member]
Defined benefit plan, fair value of plan assets	107.5	99.8
Government Debt Securities [Member]
Defined benefit plan, fair value of plan assets	38.1	32.9
Other Assets [Member]
Defined benefit plan, fair value of plan assets	0.8	0.6
Guaranteed Investments Contracts [Member]
Defined benefit plan, fair value of plan assets	13.9	14.2
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined benefit plan, fair value of plan assets	254.7	251.8
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Cash and Cash Equivalents [Member]
Defined benefit plan, fair value of plan assets	0.2	0.3
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fund Investments [Member]
Defined benefit plan, fair value of plan assets	134.1	140.5
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Equity securities [Member]
Defined benefit plan, fair value of plan assets	107.5	99.8
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Government Debt Securities [Member]
Defined benefit plan, fair value of plan assets	12.1	10.6
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Other Assets [Member]
Defined benefit plan, fair value of plan assets	0.8	0.6
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Guaranteed Investments Contracts [Member]
Defined benefit plan, fair value of plan assets	0	0
Significant Other Observable Inputs (Level 2) [Member]
Defined benefit plan, fair value of plan assets	26.0	22.3
Significant Other Observable Inputs (Level 2) [Member] | Cash and Cash Equivalents [Member]
Defined benefit plan, fair value of plan assets	0	0
Significant Other Observable Inputs (Level 2) [Member] | Fund Investments [Member]
Defined benefit plan, fair value of plan assets	0	0
Significant Other Observable Inputs (Level 2) [Member] | Equity securities [Member]
Defined benefit plan, fair value of plan assets	0	0
Significant Other Observable Inputs (Level 2) [Member] | Government Debt Securities [Member]
Defined benefit plan, fair value of plan assets	26.0	22.3
Significant Other Observable Inputs (Level 2) [Member] | Other Assets [Member]
Defined benefit plan, fair value of plan assets	0	0
Significant Other Observable Inputs (Level 2) [Member] | Guaranteed Investments Contracts [Member]
Defined benefit plan, fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) [Member]
Defined benefit plan, fair value of plan assets	13.9	14.2	13.9
Significant Unobservable Inputs (Level 3) [Member] | Cash and Cash Equivalents [Member]
Defined benefit plan, fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) [Member] | Fund Investments [Member]
Defined benefit plan, fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) [Member] | Equity securities [Member]
Defined benefit plan, fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) [Member] | Government Debt Securities [Member]
Defined benefit plan, fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) [Member] | Other Assets [Member]
Defined benefit plan, fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) [Member] | Guaranteed Investments Contracts [Member]
Defined benefit plan, fair value of plan assets	$ 13.9	$ 14.2