Leases (Sale and Leaseback Agreement) (Details) (USD $) In Millions, unless otherwise specified	0 Months Ended	1 Months Ended
May 03, 2013 acre Building	Jul. 26, 2013 Building
May 2013 Sales Lease Back Agreement
Sale Leaseback Transaction [Line Items]
Area of land	18
Number of real estate properties	4
Period to complete transaction	6 years
Number of buildings leased back		3
Number of buildings sold		2
Proceeds from sale		$ 83
Fairfax County, Virginia, Two Office Buildings
Sale Leaseback Transaction [Line Items]
Proceeds from sale		40
Book value of the building sold		42
Net loss on sales and disposals of assets		2
Term of lease		P6M
Notes Payable, Other Payables
Sale Leaseback Transaction [Line Items]
Term of debt instrument		7 years
Rate of interest		3.70%
Other Long-term Liabilities \| Multi-level Parking Garage
Sale Leaseback Transaction [Line Items]
Allocated consideration to Note parable and Other long-term liabilities		1
Other Long-term Liabilities \| Surface Parking Lots
Sale Leaseback Transaction [Line Items]
Allocated consideration to Note parable and Other long-term liabilities		4
Notes payable and long-term debt, net of current portion \| Notes Payable, Other Payables
Sale Leaseback Transaction [Line Items]
Allocated consideration to Note parable and Other long-term liabilities		$ 38

Sale Leaseback Transaction, Number of Buildings Leased Back

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- Definition

Sale of Property, Period to Complete Transaction

+ References

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- Definition

Sales and Leaseback Transaction, Number of Buildings Sold

+ References

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- Definition

Area of land held.

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- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

Amount of gain (loss) on sale or disposal of property, plant and equipment assets, excluding oil and gas property and timber property.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 360

-SubTopic 10

-Section 50

-Paragraph 3

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The number of real estate properties owned as of the balance sheet date.

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- Definition

The liability due as of the balance sheet date for leasebacks accounted for using the deposit method.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 10

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- Definition

The financing cost related to leases that have been recorded under the deposit method, as a financing or as a capital leases in connection with the transaction involving the sale of property to another party and the lease of the property back to the seller.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Imputed Interest Rate

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- Definition

A description of the terms of the lease(s) related to the assets being leased-back in connection with the transaction involving the sale of property to another party and the lease of the property back to the seller.

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- Definition

The net book value of the asset(s) sold in connection with the sale of the property to another party and lease back to the seller.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

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- Definition

Amount of cash inflow after closing and deferred financing costs received by a seller-lessee in a sale-leaseback recognized in financing activities.

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