| **Stock-based compensation plans (Narrative) (Details) (USD $)In Millions, except Share data, unless otherwise specified**                                         | 12 Months Ended |        |         |           | 12 Months Ended |           |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------|--------|---------|-----------|-----------------|-----------|
||
| **Share-based Compensation Arrangement by Share-based Payment Award [Line Items]**                                                                                 |            |   |    |      |            |      |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period                                                                            |            |   |    |      |            |      |   | 3 years |   |   |   |   | 3 years |   |   |   |   |   |   |   |   |
| Share-based Compensation Arrangement by Share-based Payment Award, Expiration Date                                                                                 |            |   |    |      |            |      |   |   |   |   | 10 years | 7 years |   |   |   |   |   |   |   |   |   |
| Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized                                                                     |            |   |    | 5,750,000 |            | 3,250,000 |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Share-based Compensation Arrangement by Share-based Payment Award, Additional Number of Shares Authorized                                                          |            |   |    |      | 2,500,000       |      |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant                                                            |            |   |    | 2,710,359 |            |      |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Outstanding Number                                       |            |   |    |      |            |      | 27,671 |   |   |   |   |   | 89,112 |   |   |   |   |   |   |   |   |
| Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested, Number Of Common Stock Delivered                 |            |   |    |      |            |      | 1 |   |   |   |   |   | 1 |   |   |   |   |   |   |   |   |
| Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested, Number Of Common Stock Delivered Period          |            |   |    |      |            |      | 10 days |   |   |   |   |   | 10 days |   |   |   |   |   |   |   |   |
| Deferred Compensation Arrangement with Individual, Shares Outstanding                                                                                              |            |   |    |      |            |      |   |   |   |   |   |   |   |   |   |   |   |   |   |   | 42,267 |
| Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value                               | $ 26.40         | $ 18   | $ 10.35 |      |            |      |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Total Intrinsic Value                                             | $ 38            | $ 20   | $ 14    |      |            |      |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Dividend yield                                                                                                                                                     | 0.00%           |   |    |      |            |      |   | 0.00% | 0.00% | 0.00% |   |   |   |   |   |   |   |   |   |   |   |
| Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Total Fair Value                       |            |   |    |      |            |      |   |   |   |   |   |   |   | 20 | 9 | 9 |   |   |   |   |   |
| Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period                                         |            |   |    |      |            |      |   |   |   |   |   |   |   |   |   |   | 149,620 | 0 | 0 | 225,000 |   |
| Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value |            |   |    |      |            |      |   |   |   |   |   |   |   |   |   |   | $ 84.75 |   |   | $ 59.25 |   |
| Expected volatility                                                                                                                                                |            |   |    |      |            |      |   | 46.80% | 52.60% | 47.30% |   |   |   |   |   |   | 47.30% |   |   |   |   |
| Risk-free interest rate                                                                                                                                            |            |   |    |      |            |      |   | 2.27% | 2.72% | 1.34% |   |   |   |   |   |   | 2.03% |   |   |   |   |
| Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period                                         |            |   |    |      |            |      |   |   |   |   |   |   |   |   |   |   | 0 |   |   | 90,000 |   |
| Share-based Compensation                                                                                                                                           | 36              | 24     | 16      |      |            |      |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized                                                            | 29              |   |    |      |            |      |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition                                    | 2               |   |    |      |            |      |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Proceeds from exercise of stock options                                                                                                                            | 40              | 30     | 13      |      |            |      |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Employee Service Share-based Compensation, Cash Flow Effect, Cash Used to Settle Awards                                                                            |            |   |    |      |            |      |   |   |   |   |   |   |   |   |   |   |   |   |   | 5 |   |
| Tax Benefit from Stock Options Exercised                                                                                                                           | 0               | 0      | 0       |      |            |      |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Redeemable equity securities modification                                                                                                                          |            |   | $ 130   |      |            |      |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |

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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
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| - Definition
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| - Definition
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| - Definition
Aggregate cash paid by the entity during the period to settle equity instruments granted under equity-based payment arrangements.
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Aggregate proceeds received by the entity during the annual period from exercises of stock or unit options and conversion of similar instruments granted under equity-based payment arrangements.
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| - Definition
As of the balance sheet date, the aggregate unrecognized cost of equity-based awards made to employees under equity-based compensation awards that have yet to vest.
+ References
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, using a decimal to express in number of years.
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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The number of shares issued in connection with an own-share lending arrangement entered into by the entity, in contemplation of a convertible debt offering or other financing.
+ References
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The difference between the carrying amount of a financial instrument subject to a registration payment arrangement recorded as temporary equity prior to adoption of FSP EITF 00-19-2 and the carrying amount reclassified to permanent equity upon the adoption of FSP EITF 00-19-2. Recorded as a cumulative effect adjustment to the beginning balance of retained earnings. Does not apply to registration payment arrangements that are no longer outstanding upon adoption of FSP EITF 00-19-2.
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The aggregate amount of noncash, equity-based employee remuneration. This may include the value of stock or unit options, amortization of restricted stock or units, and adjustment for officers' compensation. As noncash, this element is an add back when calculating net cash generated by operating activities using the indirect method.
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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The date when the equity-based award expires as specified in the award agreement, which may be presented in a variety of ways (for example, year, month and year, day, month and year, quarter of a year).
+ References
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Description of the period of time over which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, which may be expressed in a variety of ways (for example, in years, month and year).
+ References
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).
+ References
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).
+ References
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.
+ References
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The total fair value of equity-based awards for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.
+ References
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.
+ References
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.
+ References
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| - Definition
The risk-free interest rate assumption that is used in valuing an option on its own shares.
+ References
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| - Definition
The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).
+ References
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| - Definition
The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.
+ References
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| - Definition
The total accumulated difference between fair values of underlying shares on dates of exercise and exercise price on options which were exercised (or share units converted) into shares during the reporting period under the plan.
+ References
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| - Definition
The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.
+ References
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| - Definition
Reductions in the entity's income taxes that arise when compensation cost (from non-qualified stock options) recognized on the entity's tax return exceeds compensation cost from non-qualified stock options recognized on the income statement. This element increases net cash provided by operating activities.
+ References
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