Business Developments And Risks And Uncertainties (Narrative) (Detail) $ in Millions		6 Months Ended
Feb. 10, 2021 USD ($)	Jun. 30, 2021 USD ($) segments
Business Acquisition [Line Items]
Number of operating segments \| segments		3
Federal legislation passed to combat the economic impact		$ 2,700,000
New relief plan proposed to stabilize the financial system		1,900,000
Aid allocated to state and local governments		350,000
Credit Suisse [Member]
Business Acquisition [Line Items]
Damages Paid Value	$ 600
Damages Sought Value		604
GFL Medium Term Notes [Member]
Business Acquisition [Line Items]
Debt instrument, Repurchase amount		$ 63
Percentage of weighted average cost of notes repurchased		78.00%
Puerto Rico [Member]
Business Acquisition [Line Items]
Claims payments		$ 277
Outstanding bonds		2,900
MBIA Corp Financing Facility [Member]
Business Acquisition [Line Items]
Payment for Debt Extinguishment or Debt Prepayment Cost		$ 150
Debt Instrument, Interest Rate, Stated Percentage		12.00%
Debt Instrument, Maturity Date		Jan. 20, 2022
Long-term Debt		$ 130

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Federal legislation passed to combat the economic impact.

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New relief plan proposed.

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