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Fair Value Option - Additional Information (Detail) - USD ($)	Jun. 30, 2019	Dec. 31, 2018
Corporate Bonds
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value of financial instruments more than one day past due	$ 0	$ 0
Fair value of financial instruments with non-accrual status	0	0
Loans and Receivables
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value of financial instruments more than one day past due	0	0
Fair value of financial instruments with non-accrual status	$ 0	$ 0

X

- Definition

Fair Value of Financial Instruments More Than One Day Past Due

+ References

No definition available.

+ Details

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Balance Type:	debit
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X

- Definition

Investment Securities Fair Value Disclosure On Nonaccrual Status

+ References

No definition available.

+ Details

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Namespace Prefix:	bx_
Data Type:	xbrli:monetaryItemType
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X

- Definition

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.

+ References

No definition available.

+ Details

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- Details

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Namespace Prefix:
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Period Type:

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- Details

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