Treasury Stock - Additional Information (Detail) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Equity, Class of Treasury Stock [Line Items]
Treasury stock, shares	6,405,000us-gaap_TreasuryStockShares	6,405,000us-gaap_TreasuryStockShares
Treasury stock, cost	475,184,000us-gaap_TreasuryStockValue	$ 475,184,000us-gaap_TreasuryStockValue
Two Thousand Five Share Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Shares repurchased program expiration date	Apr. 29, 2018
Two Thousand Five Share Repurchase Program \| Class A
Equity, Class of Treasury Stock [Line Items]
Stock authorized to repurchase by board of directors	800,000,000
Treasury stock, shares	3,826,947
Shares repurchased, average price per share	90.23
Treasury stock, cost	345,300,000

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Amount of stock repurchase plan authorized.

+ References

No definition available.

+ Details

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- Definition

Expiration date for the purchase of an entity's own shares under a stock repurchase plan, in the CCYY-MM-DD format.

+ References

No definition available.

+ Details

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- Definition

Total cost of shares repurchased divided by the total number of shares repurchased.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 30

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6405813&loc=d3e23239-112655

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- Definition

Number of common and preferred shares that were previously issued and that were repurchased by the issuing entity and held in treasury on the financial statement date. This stock has no voting rights and receives no dividends.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.28,29)

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

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 29, 30

-Article 5

+ Details

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- Definition

The amount allocated to treasury stock. Treasury stock is common and preferred shares of an entity that were issued, repurchased by the entity, and are held in its treasury.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 30

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=6405834&loc=d3e23315-112656

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