Fair value measurements - Narrative (Detail)	1 Months Ended
Dec. 31, 2017 USD ($)
RBI [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment redeemed, face amount	$ 3,000,000,000

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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