INDEBTEDNESS - Facilities Narrative (Details) - USD ($)	1 Months Ended	3 Months Ended		9 Months Ended
INDEBTEDNESS - Facilities Narrative (Details) - USD ($)	May 31, 2020	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Revolving Credit Facility \| 2020 Credit Facility \| Line of Credit
Debt Instrument [Line Items]
Remaining borrowing capacity	$ 775,000,000
Debt covenant, minimum quarterly liquidity amount	$ 250,000,000
Amounts drawn to date		$ 0		$ 0
Letters of credit outstanding		0		$ 0
Revolving Credit Facility \| 2020 Credit Facility \| Line of Credit \| Secured Overnight Financing Rate (SOFR)
Debt Instrument [Line Items]
Basis spread on variable rate (as percent)				1.00%
Revolving Credit Facility \| 2020 Credit Facility \| Line of Credit \| Prime Rate
Debt Instrument [Line Items]
Basis spread on variable rate (as percent)				0.50%
Revolving Credit Facility \| 2020 Credit Facility \| Line of Credit \| Federal Funds Rate
Debt Instrument [Line Items]
Basis spread on variable rate (as percent)				0.50%
Revolving Credit Facility \| 2020 Credit Facility \| Line of Credit \| Minimum
Debt Instrument [Line Items]
Unused commitment fee percentage	0.10%
Revolving Credit Facility \| 2020 Credit Facility \| Line of Credit \| Minimum \| Secured Overnight Financing Rate (SOFR)
Debt Instrument [Line Items]
Basis spread on variable rate (as percent)				1.25%
Additional basis spread on variable rate (as percent)				0.25%
Revolving Credit Facility \| 2020 Credit Facility \| Line of Credit \| Minimum \| Prime Rate
Debt Instrument [Line Items]
Additional basis spread on variable rate (as percent)				0.25%
Revolving Credit Facility \| 2020 Credit Facility \| Line of Credit \| Minimum \| Federal Funds Rate
Debt Instrument [Line Items]
Additional basis spread on variable rate (as percent)				0.25%
Revolving Credit Facility \| 2020 Credit Facility \| Line of Credit \| Maximum
Debt Instrument [Line Items]
Unused commitment fee percentage	0.20%
Revolving Credit Facility \| 2020 Credit Facility \| Line of Credit \| Maximum \| Secured Overnight Financing Rate (SOFR)
Debt Instrument [Line Items]
Basis spread on variable rate (as percent)				1.75%
Additional basis spread on variable rate (as percent)				0.75%
Revolving Credit Facility \| 2020 Credit Facility \| Line of Credit \| Maximum \| Prime Rate
Debt Instrument [Line Items]
Additional basis spread on variable rate (as percent)				0.75%
Revolving Credit Facility \| 2020 Credit Facility \| Line of Credit \| Maximum \| Federal Funds Rate
Debt Instrument [Line Items]
Additional basis spread on variable rate (as percent)				0.75%
Line of Credit \| Warehouse Funding Facilities \| Secured Debt
Debt Instrument [Line Items]
Remaining borrowing capacity		983,100,000		$ 983,100,000
Amounts drawn to date		501,000,000.0		501,000,000.0
Maximum borrowing capacity		1,500,000,000		1,500,000,000
Interest expense		$ 10,700,000	$ 16,400,000	$ 36,500,000	$ 52,300,000

Block, Inc. 10-Q