Employee Benefits Defined benefit plans disclosures (Details)	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010
Actual Allocation [Abstract]
Total domestic equity securities (in hundredths)	35.00%	41.00%
Foreign equity securities [Abstract]
Developed market foreign equity securities (in hundredths)	20.00%	25.00%
Emerging market foreign equity securities (in hundredths)	4.00%	7.00%
Total foreign securities (in hundredths)	24.00%	32.00%
Debt securities [Abstract]
Investment grade intermediate term debt (in hundredths)	5.00%	4.00%
Investment grade long-term debt (in hundredths)	17.00%	13.00%
Below-investment grade debt (in hundredths)	9.00%	9.00%
Total debt securities (in hundredths)	31.00%	26.00%
Cash and short-term investments (in hundredths)	1.00%	1.00%
Inflation protection securities (in hundredths)	9.00%	0.00%
Policy Range [Abstract]
Total domestic equity securities - minimum range (in hundredths)	35.00%	35.00%
Total domestic equity securities - maximum range (in hundredths)	45.00%	45.00%
Foreign equity securities [Abstract]
Total foreign securities - minimum range (in hundredths)	25.00%	25.00%
Total foreign securities - maximum range (in hundredths)	35.00%	35.00%
Debt securities [Abstract]
Total debt securities - minimum range (in hundredths)	25.00%	25.00%
Total debt securities - maximum range (in hundredths	35.00%	35.00%
Cash and short-term investments - minimum range (in hundredths)	0.00%	0.00%
Cash and short-term investments - maximum range (in hundredths)	3.00%	3.00%
Total debt securities [Abstract]
Average maturities for investment grade intermediate term debt (in years)	5 - 10Y
Average maturities for investment grade long-term debt (in years)	More than 10 years
Average maturities for below-investment grade debt (in years)	Up to 10 years
Time over which set performance objectives for each investment manager is expected to be met	A three-year period or complete market cycle, whichever is shorter

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- Definition

Disclosure of additional asset categories and additional information about specific assets within a category that is useful in understanding the risks associated with each asset category and the overall expected long-term rate of return on assets, specifically the average maturities of the investment in years.

+ References

No definition available.

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No definition available.

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This element represents the period of time in which set performance objectives for each investment manager is expected to be met.

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No definition available.

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- Definition

The percentage of the fair value of below-investment grade debt securities to the fair value of total plan assets held as of the measurement date.

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No definition available.

+ Details

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- Definition

This element represents the total percentage of the fair value of cash and short-term investments, to the fair value of total plan assets held as of the measurement date.

+ References

No definition available.

+ Details

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- Definition

This element represents the percentage of the fair value of foreign emerging market equity securities, to the fair value of total plan assets held as of the measurement date.

+ References

No definition available.

+ Details

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- Definition

This element represents the percentage of the fair value of foreign equity securities, to the fair value of total plan assets held as of the measurement date.

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No definition available.

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- Definition

This element represents the total percentage of the fair value of foreign securities, to the fair value of total plan assets held as of the measurement date.

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No definition available.

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- Definition

This element represents the total percentage of the fair value of inflation protection securities, to the fair value of total plan assets held as of the measurement date.

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No definition available.

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- Definition

The percentage of the fair value of investment grade intermediate term debt securities to the fair value of total plan assets held as of the measurement date.

+ References

No definition available.

+ Details

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- Definition

The percentage of the fair value of investment grade long-term debt securities to the fair value of total plan assets held as of the measurement date.

+ References

No definition available.

+ Details

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- Definition

Target allocation percentage of investments in cash and short-term investments to total plan assets presented on a weighted-average basis as of the measurement date of the latest statement of financial position.

+ References

No definition available.

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- Definition

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- Definition

Target allocation maximum percentage of investments in foreign securities to total plan assets presented on a weighted-average basis as of the measurement date of the latest statement of financial position.

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No definition available.

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- Definition

Target allocation minimum percentage of investments in foreign securities to total plan assets presented on a weighted-average basis as of the measurement date of the latest statement of financial position.

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No definition available.

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- Definition

The percentage of the fair value of debt securities to the fair value of total plan assets held as of the measurement date.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph d(1)

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- Definition

The percentage of the fair value of equity securities to the fair value of total plan assets held as of the measurement date.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph d(1)

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- Definition

Target allocation maximum percentage of investments in debt securities to total plan assets presented on a weighted-average basis as of the measurement date of the latest statement of financial position.

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No definition available.

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- Definition

Target allocation minimum percentage of investments in debt securities to total plan assets presented on a weighted-average basis as of the measurement date of the latest statement of financial position.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

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- Definition

Target allocation maximum percentage of investments in equity securities to total plan assets presented on a weighted-average basis as of the measurement date of the latest statement of financial position.

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No definition available.

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Target allocation minimum percentage of investments in equity securities to total plan assets presented on a weighted-average basis as of the measurement date of the latest statement of financial position.

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No definition available.

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