| **Finance receivables (Details) (USD $)**                                                                                                                                                                                                        | 3 Months Ended |     |               |     |                 |                 |              |              |               |               |               |               |               |               |             |             |             |             |             |        |        | 0 Months Ended |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------|-----|---------------|-----|-----------------|-----------------|--------------|--------------|---------------|---------------|---------------|---------------|---------------|---------------|-------------|-------------|-------------|-------------|-------------|--------|--------|----------------|
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| **Financing Receivable, Recorded Investment [Line Items]**                                                                                                                                                                                       |           |     |          |     |            |            |         |         |          |          |          |          |          |          |        |        |        |        |        |   |   |           |   |   |
| On-balance sheet assets, net of intercompany balances                                                                                                                                                                                            |           |     |          |     | $ 3,000,000,000 | $ 3,500,000,000 |         |         |          |          |          |          |          |          |        |        |        |        |        |   |   |           |   |   |
| Financing receivable, by class, number of portfolio segments                                                                                                                                                                                     | 2              |     |          |     |            |            |         |         |          |          |          |          |          |          |        |        |        |        |        |   |   |           |   |   |
| Loans and leases receivable, gross, carrying amount                                                                                                                                                                                              | 2,668,000,000  |     | 2,947,000,000 |     |            |            |         |         | 1,384,000,000 | 1,613,000,000 | 1,284,000,000 | 1,334,000,000 |          |          |        |        |        |        |        |   |   |           |   |   |
| Less: Allowance for doubtful accounts                                                                                                                                                                                                            | 28,000,000     |     | 34,000,000    |     |            |            |         |         |          |          |          |          |          |          |        |        |        |        |        |   |   |           |   |   |
| Finance receivables, net                                                                                                                                                                                                                         | 2,640,000,000  |     | 2,913,000,000 |     |            |            |         |         |          |          |          |          |          |          |        |        |        |        |        |   |   |           |   |   |
| Less: Current portion, net                                                                                                                                                                                                                       | 2,066,000,000  | [1] | 2,198,000,000 | [1] |            |            |         |         |          |          |          |          |          |          |        |        |        |        |        |   |   |           |   |   |
| Noncurrent portion, net                                                                                                                                                                                                                          | 574,000,000    |     | 715,000,000   |     |            |            |         |         |          |          |          |          |          |          |        |        |        |        |        |   |   |           |   |   |
| Facility                                                                                                                                                                                                                                         |           |     |          |     |            |            |         |         |          |          |          |          | 1,074,000,000 | 1,100,000,000 | 500,000,000 | 500,000,000 | 350,000,000 | 350,000,000 | 224,000,000 | 0      | 0      | 250,000,000    | 125,000,000 |   |
| Unutilized funding                                                                                                                                                                                                                               |           |     |          |     |            |            | 29,000,000   | 9,000,000    |          |          |          |          |          |          | 320,000,000 | 170,000,000 |        |        |        |   |   |           |   |   |
| Proceeds from Issuance of Senior Long-term Debt                                                                                                                                                                                                  |           |     |          |     |            |            |         |         |          |          |          |          |          |          |        |        |        |        |        |   |   |           |   | 224,000,000 |
| Funding facility collateral, retail accounts                                                                                                                                                                                                     |           |     |          |     |            |            | 209,000,000  | 174,000,000  |          |          |          |          |          |          |        |        |        |        |        |   |   |           |   |   |
| Funding facility collateral, cash equivalents                                                                                                                                                                                                    |           |     |          |     |            |            | $ 31,000,000 | $ 33,000,000 |          |          |          |          |          |          |        |        |        |        |        |   |   |           |   |   |
|                                                                                                                                                                                                                                                  |
| [1]The current portion of finance receivables is computed based on contractual maturities. Actual cash collections typically vary from the contractual cash flows because of prepayments, extensions, delinquencies, credit losses, and renewals |

| X                                                                                                                                                                                                                                                      |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Assets Net Of Intercompany Balances
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Reflects carrying amount of all categories of loans and leases held in portfolio, net of unearned income and the allowance for losses on loans and leases, due from customers, clients, lessees, borrowers, or others more than one year from the balance sheet date (or the normal operating cycle, whichever is longer).
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| - Definition
Finance Receivables Retail Accounts Collateral For Borrowed Securities
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| X                                                                                                                                                                                                                                                                                              |
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| - Definition
Financing Receivable By Class Number of Portfolio Segments
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Carrying amount as of the balance sheet date of cash collateral held for borrowed securities, for which the cash is restricted as to withdrawal or usage.
+ References
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The stated principal amount of the debt instrument at time of issuance, which may vary from the carrying amount because of unamortized premium or discount.
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of unused borrowing capacity under the long-term financing arrangement that is available to the entity as of the balance sheet date.
+ References
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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of the recorded investment in a contractual right to receive money on demand or on fixed or determinable dates that is recognized as an asset in the creditor's statement of financial position. Examples include, but are not limited to, accounts receivable (with terms exceeding one year), notes receivable and receivables relating to lessor's rights to payments from leases other than operating leases that have been recorded as assets.
+ References
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The allowance for loan and lease losses represents the reserve to cover probable credit losses related to specifically identified loans and leases, as well as probable credit losses inherent in the remainder of the loan portfolio as of the balance sheet date. For banks, include currently required allocated transfer risk reserves. Include carryover of or adjustments to the allowance for loan losses in connection with business combinations determined to be appropriate.
+ References
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|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Reflects the aggregate gross carrying amount of all categories of loans and leases held in portfolio, prior to deducting deferred income and the allowance for losses on loans and leases.
+ References
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Reflects the aggregate carrying amount of all categories of loans and leases held in portfolio, net of unearned income and the allowance for losses on loans and leases.
+ References
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The cash inflow from a borrowing with the highest claim on the assets of the entity in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle, if longer).
+ References
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