Retirement Benefit Plans (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined benefit plan, cost recognized	$ 57.4	$ 54.3	$ 54.2
Other postretirement benefits payable	25.4	21.8
Cash investments in time deposits	3.8ivz_CashInvestmentsInTimeDeposits	4.1ivz_CashInvestmentsInTimeDeposits
Retirement Plans [Member]
Estimated amounts of contributions expected to be paid to the plans in next fiscal year	15.2
Medical Plans [Member]
Estimated amounts of contributions expected to be paid to the plans in next fiscal year	$ 0

Cash Investments In Time Deposits

No definition available.

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Balance Type:	debit
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- Definition

Amount of employer's best estimate of contributions expected to be paid to the plan during the next fiscal year beginning after the date of the latest statement of financial position.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (g)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

+ Details

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- Definition

The amount of the cost recognized during the period for defined contribution plans.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 70

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6414718&loc=d3e28014-114942

+ Details

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- Definition

The total amount of the entity's obligation as of the balance sheet date under any other retirement plan(s), such as one or more defined contribution plans.

+ References

No definition available.

+ Details

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- Details

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- Details

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