Consolidated Statement of Changes in Shareholders' Equity (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Common stock
Balance, beginning of year	$ 21,500us-gaap_CommonStockValueOutstanding	$ 21,161us-gaap_CommonStockValueOutstanding	$ 20,732us-gaap_CommonStockValueOutstanding
Employee share-based compensation	149	158	261
Compensation amortization under share-based plans and other changes	194	181	168
Balance, end of year	21,843us-gaap_CommonStockValueOutstanding	21,500us-gaap_CommonStockValueOutstanding	21,161us-gaap_CommonStockValueOutstanding
Retained earnings
Balance, beginning of year	24,291	21,352	19,579
Net income	3,692us-gaap_ProfitLoss	3,673us-gaap_ProfitLoss	2,473us-gaap_ProfitLoss
Dividends	(735)us-gaap_Dividends	(734)us-gaap_Dividends	(700)us-gaap_Dividends
Other	3trv_RetainedEarningsOther
Balance, end of year	27,251	24,291	21,352
Accumulated other comprehensive income, net of tax
Balance, beginning of year	810	2,236	2,005
Other comprehensive income (loss)	70	(1,426)	231
Balance, end of year	880	810	2,236
Treasury stock (at cost)
Balance, beginning of year	(21,805)us-gaap_TreasuryStockValue	(19,344)us-gaap_TreasuryStockValue	(17,839)us-gaap_TreasuryStockValue
Treasury stock acquired - share repurchase authorization	(3,275)	(2,400)	(1,450)
Net shares acquired related to employee share-based compensation plans	(58)	(61)	(55)
Balance, end of year	(25,138)us-gaap_TreasuryStockValue	(21,805)us-gaap_TreasuryStockValue	(19,344)us-gaap_TreasuryStockValue
Total shareholders' equity	$ 24,836	$ 24,796	$ 25,405
Common shares outstanding
Balance, beginning of year	353.5us-gaap_CommonStockSharesOutstanding	377.4us-gaap_CommonStockSharesOutstanding	392.8us-gaap_CommonStockSharesOutstanding
Treasury stock acquired - share repurchase authorization	(35.1)	(28.4)	(22.4)
Net shares issued under employee share-based compensation plans	3.8	4.5	7.0
Balance, end of year	322.2us-gaap_CommonStockSharesOutstanding	353.5us-gaap_CommonStockSharesOutstanding	377.4us-gaap_CommonStockSharesOutstanding

Number of net shares issued during the period for share-based compensation.

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Number of shares that have been repurchased during the period as part of the share repurchase program.

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This element represents the amount of compensation amortization under share-based compensation plans and other changes recognized as expense in the income statement.

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Changes to retained earnings not separately identified on the Statement of Shareholders' Equity, including minority Interest.

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Value of stock that has been repurchased during the period as part of the share repurchase program.

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Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

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The amount of adjustment to stockholders' equity associated with an employee's income tax withholding obligation as part of a net-share settlement of a share-based award.

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Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

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Value of all classes of common stock held by shareholders. May be all or portion of the number of common shares authorized. These shares exclude common shares repurchased by the entity and held as treasury shares.

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Amount of paid and unpaid cash, stock, and paid-in-kind (PIK) dividends declared, for example, but not limited to, common and preferred stock.

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Amount after tax and reclassification adjustments of other comprehensive income (loss).

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The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest.

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Amount of stockholders' equity (deficit), net of receivables from officers, directors, owners, and affiliates of the entity, attributable to both the parent and noncontrolling interests. Amount excludes temporary equity. Alternate caption for the concept is permanent equity.

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Value of stock (or other type of equity) issued during the period as a result of any equity-based compensation plan other than an employee stock ownership plan (ESOP), net of stock value of such awards forfeited. Stock issued could result from the issuance of restricted stock, the exercise of stock options, stock issued under employee stock purchase plans, and/or other employee benefit plans.

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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.

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