Employee Benefit Plans (Details 3) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Share-Based Compensation Expense
Recurring amortization	$ 6	$ 5	$ 6
Accelerated amortization for retirement eligible employees	1	5	6
Share-based compensation expense including capitalized as DAC	8	11	13
Less: Share-based compensation capitalized as DAC	(1)	(3)	(2)
Share-based compensation expense	7.0	8.0	11.0
Income tax benefit	2	2	2
Employee
Share-Based Compensation Expense
Share-based compensation expense including capitalized as DAC	7	10	12
Directors
Share-Based Compensation Expense
Share-based compensation expense including capitalized as DAC	1	1	1
Stock Purchase Plan
Share-Based Compensation Expense
Share-based compensation expense	0.2	0.2	0.3
Stock Purchase Plan \| Employee
Share-Based Compensation Expense
Share-based compensation expense including capitalized as DAC	0	0	0
Restricted Stock Awards \| Employee
Share-Based Compensation Expense
Share-based compensation expense including capitalized as DAC	7	10	12
Restricted Stock Awards \| Directors
Share-Based Compensation Expense
Share-based compensation expense including capitalized as DAC	1	1	1
Restricted Stock Units \| Directors
Share-Based Compensation Expense
Share-based compensation expense including capitalized as DAC	0	0	0
Stock Options \| Directors
Share-Based Compensation Expense
Share-based compensation expense including capitalized as DAC	$ 0	$ 0	$ 0

Allocated Share-based Compensation Expense, Including Capitalized Amount

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- Definition

Represents the amount of accelerated amortization of share-based compensation cost for retirement eligible employees.

+ References

No definition available.

+ Details

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- Definition

Represents the amount of recurring amortization of share-based compensation cost.

+ References

No definition available.

+ Details

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- Definition

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (h)(1)(i)

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph g(1)

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 1

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-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 14

-Section F

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph 64

-Subparagraph b

-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 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

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-Paragraph 1

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Represents the compensation cost capitalized during the period arising from equity-based compensation arrangements (for example, shares of stock, units, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph g(1)

-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 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (h)(1)(ii)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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- Definition

The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

+ References

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