The percentage points added to the reference rate to compute the variable rate on the debt instrument.

No definition available.

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Date that the debt agreement requires the first payment to be made, which may be presented in a variety of ways (year, month and year, day, month and year, quarter, etc.).

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 470

-Section 50

-Paragraph 3

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6479336&loc=d3e64711-112823

+ Details

Name:	us-gaap_DebtInstrumentDateOfFirstRequiredPayment
Namespace Prefix:	us-gaap_
Data Type:	us-types:dateStringItemType
Balance Type:	na
Period Type:	duration

- Definition

The stated principal amount of the debt instrument at time of issuance, which may vary from the carrying amount because of unamortized premium or discount.

+ References

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

-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 21

-Paragraph 16, 20

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 55

-Paragraph 8

-URI http://asc.fasb.org/extlink&oid=6584090&loc=d3e28878-108400

+ Details

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Date when the debt instrument was issued, which may be presented in a variety of ways (year, month and year, day, month and year, quarter, etc.).

+ References

+ Details

Name:	us-gaap_DebtInstrumentIssuanceDate
Namespace Prefix:	us-gaap_
Data Type:	us-types:dateStringItemType
Balance Type:	na
Period Type:	duration

- Definition

Date when the debt instrument is scheduled to be fully repaid, which may be presented in a variety of ways (year, month and year, day, month and year, quarter, etc.).

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 129

-Paragraph 2, 4

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(2))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentMaturityDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_DebtLongtermAndShorttermCombinedAmountAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount borrowed under the credit facility as of the balance sheet date.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

+ Details

Name:	us-gaap_LineOfCreditFacilityAmountOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityCommitmentFeePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 129

-Paragraph 2, 4

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The cash inflow during the period from additional borrowings in aggregate debt. Includes proceeds from short-term and long-term debt.

+ References

No definition available.

+ Details

Name:	us-gaap_ProceedsFromIssuanceOfDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Long-term Debt (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Long-term Debt Types [Abstract]
Annual Facility Fee	0.175%
Proceeds from Issuance of Debt	$ 100.0
Bonds Face Amount	43.0
Undrawn Letters of Credit	140.2
Minimum [Member] \| Alternate Base Rate [Member]
Long-term Debt Types [Abstract]
Margin on Base Rate	0.225%
Maximum [Member] \| Alternate Base Rate [Member]
Long-term Debt Types [Abstract]
Margin on Base Rate	1.325%
Revolving Facility [Member]
Long-term Debt Types [Abstract]
Margin on Base Rate	1.75%
Unsecured notes outstanding	110.0	217.2
Annual Facility Fee	0.375%
Revolving Facility [Member] \| Minimum [Member]
Long-term Debt Types [Abstract]
Margin on Base Rate	1.225%
Annual Facility Fee	0.15%
Revolving Facility [Member] \| Maximum [Member]
Long-term Debt Types [Abstract]
Margin on Base Rate	2.325%
Annual Facility Fee	0.55%
Amended Revolving Facility [Member]
Long-term Debt Types [Abstract]
Debt Issuance or Start Date	January 06, 2012
Credit Facility Borrowing Capacity	400.0
Credit Facility Extended Borrowing Capacity	480.0
Debt Due Date	Jan. 01, 2017
Credit Facility Availble Borrowing Credit	290.0
Amended Revolving Facility [Member] \| LIBOR [Member]
Long-term Debt Types [Abstract]
Margin on Base Rate	1.20%
Amended Revolving Facility [Member] \| Minimum [Member]
Long-term Debt Types [Abstract]
Annual Facility Fee	0.10%
Amended Revolving Facility [Member] \| Minimum [Member] \| LIBOR [Member]
Long-term Debt Types [Abstract]
Margin on Base Rate	0.90%
Amended Revolving Facility [Member] \| Minimum [Member] \| Alternate Base Rate [Member]
Long-term Debt Types [Abstract]
Margin on Base Rate	0.00%
Amended Revolving Facility [Member] \| Maximum [Member]
Long-term Debt Types [Abstract]
Annual Facility Fee	0.30%
Amended Revolving Facility [Member] \| Maximum [Member] \| LIBOR [Member]
Long-term Debt Types [Abstract]
Margin on Base Rate	1.575%
Amended Revolving Facility [Member] \| Maximum [Member] \| Alternate Base Rate [Member]
Long-term Debt Types [Abstract]
Margin on Base Rate	0.575%
Private Placement Notes [Member]
Long-term Debt Types [Abstract]
Debt Due Date	Jan. 01, 2021
Debt Required Payments Start Date	Jan-15
Proceeds from Issuance of Debt	100.0
Private Placement Notes [Member] \| Private Placement Notes Series A [Member]
Long-term Debt Types [Abstract]
Unsecured notes outstanding	50.0
Private Placement Notes [Member] \| Private Placement Notes Series B [Member]
Long-term Debt Types [Abstract]
Unsecured notes outstanding	50.0
Unsecured Multi-currency Debt Facilities [Member]
Long-term Debt Types [Abstract]
Credit Facility Borrowing Capacity	70.0
Credit Facility Availble Borrowing Credit	37.0
Undrawn Letters of Credit	21.7
Unsecured Multi-currency Debt Facilities [Member] \| October 2014 Multi-currency Facility [Member]
Long-term Debt Types [Abstract]
Debt Due Date	Oct. 01, 2014
Credit Facility Availble Borrowing Credit	30.0
Unsecured Multi-currency Debt Facilities [Member] \| December 2012 Multi-currency Facility [Member]
Long-term Debt Types [Abstract]
Debt Due Date	Dec. 01, 2012
Credit Facility Availble Borrowing Credit	20.0
Unsecured Multi-currency Debt Facilities [Member] \| May 2014 Multi-currency Facility [Member]
Long-term Debt Types [Abstract]
Debt Due Date	May 01, 2014
Credit Facility Availble Borrowing Credit	20.0
Unsecured Multi-currency Debt Facilities [Member] \| Minimum [Member]
Long-term Debt Types [Abstract]
Margin on Base Rate	1.00%
Unsecured Multi-currency Debt Facilities [Member] \| Maximum [Member]
Long-term Debt Types [Abstract]
Margin on Base Rate	2.50%
Unsecured Letter of Credit Facilities [Member]
Long-term Debt Types [Abstract]
Credit Facility Borrowing Capacity	139.0
Credit Facility Availble Borrowing Credit	25.0
Undrawn Letters of Credit	114.2
Unsecured Letter of Credit Facilities [Member] \| 54 Million Unsecured Letter of Credit Facility [Member]
Long-term Debt Types [Abstract]
Debt Due Date	Dec. 01, 2014
Credit Facility Availble Borrowing Credit	54.0
Unsecured Letter of Credit Facilities [Member] \| 85 Million Unsecured Letter of Credit Facility [Member]
Long-term Debt Types [Abstract]
Debt Due Date	Jun. 01, 2015
Credit Facility Availble Borrowing Credit	85.0
Unsecured Letter of Credit Facilities [Member] \| 24 Million Unsecured Letter of Credit Facility [Member]
Long-term Debt Types [Abstract]
Debt Due Date	Dec. 01, 2014
Credit Facility Availble Borrowing Credit	24.0
Unsecured Bilateral Commited Credit Facilities [Member]
Long-term Debt Types [Abstract]
Credit Facility Borrowing Capacity	20.0
Debt Due Date	Mar. 01, 2012
Credit Facility Availble Borrowing Credit	20.0
Unsecured Bilateral Commited Credit Facilities [Member] \| Minimum [Member]
Long-term Debt Types [Abstract]
Margin on Base Rate	1.75%
Unsecured Bilateral Commited Credit Facilities [Member] \| Maximum [Member]
Long-term Debt Types [Abstract]
Margin on Base Rate	2.25%
Dominion Terminal Associates Bonds [Member]
Long-term Debt Types [Abstract]
Debt Due Date	Jan. 01, 2033
Other Credit Facilities [Member]
Long-term Debt Types [Abstract]
Undrawn Letters of Credit	$ 4.3