Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Allowance for doubtful accounts	$ 7	$ 3
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	100,000,000us-gaap_PreferredStockSharesAuthorized	100,000,000us-gaap_PreferredStockSharesAuthorized
Preferred stock, shares issued	0us-gaap_PreferredStockSharesIssued	0us-gaap_PreferredStockSharesIssued
Preferred stock, shares outstanding	0us-gaap_PreferredStockSharesOutstanding	0us-gaap_PreferredStockSharesOutstanding
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	1,600,000,000us-gaap_CommonStockSharesAuthorized	1,600,000,000us-gaap_CommonStockSharesAuthorized
Common stock, shares issued	132,315,465us-gaap_CommonStockSharesIssued	131,537,798us-gaap_CommonStockSharesIssued
Common stock, shares outstanding	130,121,292us-gaap_CommonStockSharesOutstanding	129,417,089us-gaap_CommonStockSharesOutstanding
Treasury stock, shares	2,194,173us-gaap_TreasuryStockShares	2,120,709us-gaap_TreasuryStockShares
Class B Common Stock
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	400,000,000	400,000,000
Common stock, shares issued	12,799,999	12,799,999
Common stock, shares outstanding	12,799,999	12,799,999

A valuation allowance for trade and other receivables due to an Entity within one year (or the normal operating cycle, whichever is longer) that are expected to be uncollectible.

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