Consolidated Balance Sheets (Parenthetical)	Dec. 31, 2017 £ / shares shares	Dec. 31, 2017 $ / shares shares	Dec. 31, 2016 £ / shares shares	Dec. 31, 2016 $ / shares shares
Treasury shares, shares held	11,100,000	11,100,000	7,300,000	7,300,000
Class A Ordinary Shares, U.S. [Member]
Common shares, par value \| $ / shares		$ 0.10		$ 0.10
Common shares, shares issued	447,000,000	447,000,000	310,300,000	310,300,000
Common Class B, Par Value In GBP [Member]
Common shares, par value \| £ / shares	£ 1		£ 1
Common shares, shares issued	50,000	50,000	50,000	50,000

Face amount or stated value per share of common stock.

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- Definition

Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

+ References

+ Details

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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 210.5-02.29,30)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: 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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