Common shareholder's equity, mezzanine equity, and non controlling interests - Common shareholder's equity (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Nov. 05, 2018
Common shareholder's equity
Common shares authorized	500,000,000
Common shares par value	$ 0.01
Preference shares authorized / designated	100,000,000
Preference shares par value	$ 0.01
Changes in common shareholders' equity
Shares issued beginning of the year	115,151,251	120,000,000
Shares outstanding beginning of the year	115,151,251	120,000,000
Issuance of shares to directors and employees (in shares)	111,052
Shares issued end of the year	115,262,303	120,000,000
Shares outstanding end of the year	115,262,303	120,000,000
Common dividends paid	$ 0.0	$ 0.0
Series B preference shares
Common shareholder's equity
Preference shares authorized / designated			15,000,000
Preference shares par value			$ 0.01

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Face amount or stated value per share of common stock.

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The maximum number of common shares permitted to be issued by an entity's charter and bylaws.

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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.

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

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Amount of paid and unpaid common stock dividends declared with the form of settlement in cash, stock and payment-in-kind (PIK).

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Number of new stock issued during the period.

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Per share amount of par value or stated value of stock classified as temporary equity. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable.

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The maximum number of securities classified as temporary equity that are permitted to be issued by an entity's charter and bylaws. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. If convertible, the issuer does not control the actions or events necessary to issue the maximum number of shares that could be required to be delivered under the conversion option if the holder exercises the option to convert the stock to another class of equity. If the security is a warrant or a rights issue, the warrant or rights issue is considered to be temporary equity if the issuer cannot demonstrate that it would be able to deliver upon the exercise of the option by the holder in all cases. Includes stock with put option held by ESOP and stock redeemable by holder only in the event of a change in control of the issuer.

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