Risk management and financial instruments - Financial Instruments Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Assets
Restricted cash	$ 218	$ 461
Fair value, recurring basis \| Level 1
Assets
Cash and cash equivalents	1,251	1,542
Restricted cash	218	461
Marketable securities	22	57
Fair value, recurring basis \| Level 3
Assets
Related party loans receivable	49	43
Temporary equity
Redeemable non-controlling interest	37	38
Fair value, recurring basis \| Level 2 \| Interest rate cap agreement
Assets
Interest rate cap	$ 7	$ 39

Loans Receivable, Fair Value Disclosure, Long-Term

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- Definition

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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- Definition

Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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The aggregate fair value as of the reporting date of all noncontrolling interests which are redeemable by the (parent) entity (1) at a fixed or determinable price on a fixed or determinable date, (2) at the option of the holder of the noncontrolling interest, or (3) upon occurrence of an event that is not solely within the control of the (parent) entity. This item includes noncontrolling interest holder's ownership (or holders' ownership) regardless of the type of equity interest (common, preferred, other) including all potential organizational (legal) forms of the investee entity.

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- Definition

Amount of cash and cash equivalents restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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